feat!: remove legacy handler (#9650)

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## Description

Closes: #7517 
ref: [comment](#9594 (comment))

<!-- Add a description of the changes that this PR introduces and the files that
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---

### Author Checklist

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please add links to any relevant follow up issues.*

I have...

- [x] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [x] added `!` to the type prefix if API or client breaking change
- [x] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#pr-targeting))
- [x] provided a link to the relevant issue or specification
- [ ] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules)
- [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#testing)
- [x] added a changelog entry to `CHANGELOG.md`
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [ ] updated the relevant documentation or specification
- [ ] reviewed "Files changed" and left comments if necessary
- [ ] confirmed all CI checks have passed

### Reviewers Checklist

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your handle next to the items reviewed if you only reviewed selected items.*

I have...

- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed `!` in the type prefix if API or client breaking change
- [ ] confirmed all author checklist items have been addressed 
- [ ] reviewed state machine logic
- [ ] reviewed API design and naming
- [ ] reviewed documentation is accurate
- [ ] reviewed tests and test coverage
- [ ] manually tested (if applicable)

CHANGELOG.md

@@ -58,6 +58,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 * [\#9594](https://github.com/cosmos/cosmos-sdk/pull/9594) `types/rest` package moved to `testutil/rest`.
 * [\#9432](https://github.com/cosmos/cosmos-sdk/pull/9432) `ConsensusParamsKeyTable` moved from `params/keeper` to `params/types`
 * [\#9576](https://github.com/cosmos/cosmos-sdk/pull/9576) Add debug error message to `sdkerrors.QueryResult` when enabled
+* [\#9650](https://github.com/cosmos/cosmos-sdk/pull/9650) Removed deprecated message handler implementation from the SDK modules.
 
 ### Client Breaking Changes
 

x/auth/module.go

@@ -111,8 +111,10 @@ func (AppModule) Name() string {
 // RegisterInvariants performs a no-op.
 func (AppModule) RegisterInvariants(_ sdk.InvariantRegistry) {}
 
-// Route returns the message routing key for the auth module.
-func (AppModule) Route() sdk.Route { return sdk.Route{} }
+// Deprecated: Route returns the message routing key for the auth module.
+func (AppModule) Route() sdk.Route {
+	return sdk.Route{}
+}
 
 // QuerierRoute returns the auth module's querier route name.
 func (AppModule) QuerierRoute() string {

x/auth/vesting/module.go

@@ -92,9 +92,9 @@ func NewAppModule(ak keeper.AccountKeeper, bk types.BankKeeper) AppModule {
 // RegisterInvariants performs a no-op; there are no invariants to enforce.
 func (AppModule) RegisterInvariants(_ sdk.InvariantRegistry) {}
 
-// Route returns the module's message router and handler.
+// Deprecated: Route returns the module's message router and handler.
 func (am AppModule) Route() sdk.Route {
-	return sdk.NewRoute(types.RouterKey, NewHandler(am.accountKeeper, am.bankKeeper))
+	return sdk.Route{}
 }
 
 // QuerierRoute returns an empty string as the module contains no query

x/authz/module/module.go

@@ -117,9 +117,9 @@ func (AppModule) Name() string {
 // RegisterInvariants does nothing, there are no invariants to enforce
 func (AppModule) RegisterInvariants(_ sdk.InvariantRegistry) {}
 
-// Route returns the message routing key for the staking module.
+// Deprecated: Route returns the message routing key for the authz module.
 func (am AppModule) Route() sdk.Route {
-	return sdk.NewRoute(authz.RouterKey, nil)
+	return sdk.Route{}
 }
 
 func (am AppModule) NewHandler() sdk.Handler {

x/bank/module.go

@@ -123,9 +123,9 @@ func (am AppModule) RegisterInvariants(ir sdk.InvariantRegistry) {
 	keeper.RegisterInvariants(ir, am.keeper)
 }
 
-// Route returns the message routing key for the bank module.
+// Deprecated: Route returns the message routing key for the bank module.
 func (am AppModule) Route() sdk.Route {
-	return sdk.NewRoute(types.RouterKey, NewHandler(am.keeper))
+	return sdk.Route{}
 }
 
 // QuerierRoute returns the bank module's querier route name.

x/capability/module.go

@@ -103,8 +103,10 @@ func (am AppModule) Name() string {
 	return am.AppModuleBasic.Name()
 }
 
-// Route returns the capability module's message routing key.
-func (AppModule) Route() sdk.Route { return sdk.Route{} }
+// Deprecated: Route returns the capability module's message routing key.
+func (AppModule) Route() sdk.Route {
+	return sdk.Route{}
+}
 
 // QuerierRoute returns the capability module's query routing key.
 func (AppModule) QuerierRoute() string { return "" }