reflection: remove the `func_for_method_checked` check (#51444)
Introduced in 539224f, the `func_for_method_checked` check has been used
for some of the reflection utilities like `code_typed`, but now it
appears to be outdated. E.g. previously, when provided with abstract
input types for optionally-generated functions, they would raise
unnecessary errors, even though the inference would utilize the fallback
code path. In such instances, the reflection utilities should present
what the inference would perform, instead of raising errors.
This commit simply removes the check. This works because all the
reflection utilities now internally calls the `InferenceState()`
constructor, where code generation occurs, and they gracefully handle
cases when code generation fails.
Now their behavior is more synced with the actual behavior of inference.
