Revert "Remove script class checks when getting function signature"

This reverts commit 0fef203b1f.

This introduced some other issues, as discussed in #72144.

modules/gdscript/tests/scripts/parser/features/super_class_check.gd

@@ -1,13 +0,0 @@
-# https://github.com/godotengine/godot/issues/71994
-
-func test():
-	pass
-
-class A extends RefCounted:
-	pass
-
-class B extends A:
-	# Parsing `duplicate()` here would throw this error:
-	# Parse Error: The function signature doesn't match the parent. Parent signature is "duplicate(bool = default) -> Resource".
-	func duplicate():
-		pass

modules/gdscript/tests/scripts/parser/features/super_class_check.out

@@ -1 +0,0 @@
-GDTEST_OK