refactor(Keys_Incoming): Appsiloed incoming key is useless

[LHerskind]

The app-siloed incoming viewing key is currently completely useless and a waste of constraints.

The non-hardened keys allow anyone with knowledge of an app siloed incoming viewing secret key to derive the incoming master key. Making it completely useless.

In #6432 I chose to bypass the computation and extra constraints. The code is still there but the functions are just exiting early returning the input keys. Kept like that so it did not require any plumbing changes.

[iAmMichaelConnor]

It it known

(from the original diagram)

[nventuro]

Closing as this is now deleted.