chore: cleanup TODOs and deprecate bad functions

[austinabell]

Cleanup getting ready for stable 4.0

• Adds missing pattern for testing_env! macro
• Deprecate setup functions that are either not needed or a foot gun because of side effects

ref #494

[ChaoticTempest]

LGTM:

error[E0133]: call to unsafe function is unsafe and requires unsafe function or block
--
--> /host/near-sdk/src/environment/env.rs:494:5
\|
494 \|     core::arch::wasm32::unreachable();
\|     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ call to unsafe function
\|
= note: consult the function's documentation for information on how to avoid undefined behavior

So it looks like the docker image still needs to get updated