Remove soft return types

[HolonProduction]

What problem(s) does this PR solve?

• Followup to GDScript: Check for soft function return types in various places #121322
• Reduces analyzer complexity by getting rid of timing related function typing and some soft type occurences

The above PR did check for soft return types in places that were consistently effected by them.
This PR completely removes soft types from return types, this is more risky than the above change and is bound to change behavior of some warnings. I'd hope to get this in early for 4.9.

However everything effected by this PR was previously dependent on function order (see the timing explanation from #121322 (comment)), which is why I don't consider this an issue. In addition the soft type deduction was bugged anyway which makes those warning not very reliable in the first place (only taking the last return statement into consideration).

Additional information

Here's an example were behaviour changes:

func a():
	return 2

func b():
	var _c = a() / 1 # This did previously emit an integer division warning. It now doesn't.

However

func b():
	var _c = a() / 1 # This did previously not emit a warning. Only the function order changed.

func a():
	return 2