Revert "Add UID support to GDScript files"

This reverts commit c7f68a27ec.

We still think GDScript files need UIDs to allow safe refactoring,
but we're still debating what form those should take exactly.

So far there seems to be agreement that it shouldn't be done via an
annotation as implemented here, so we're reverting this one for now,
to revisit the feature in a future PR.

modules/gdscript/tests/scripts/parser/errors/uid_duplicate.gd

@@ -1,5 +0,0 @@
-@uid("uid://c4ckv3ryprcn4")
-@uid("uid://c4ckv3ryprcn4")
-
-func test():
-    pass

modules/gdscript/tests/scripts/parser/errors/uid_duplicate.out

@@ -1,2 +0,0 @@
-GDTEST_PARSER_ERROR
-"@uid" annotation can only be used once.

modules/gdscript/tests/scripts/parser/errors/uid_invalid.gd

@@ -1,4 +0,0 @@
-@uid("not a valid uid")
-
-func test():
-    pass

modules/gdscript/tests/scripts/parser/errors/uid_invalid.out

@@ -1,2 +0,0 @@
-GDTEST_PARSER_ERROR
-The annotated UID is invalid.

modules/gdscript/tests/scripts/parser/errors/uid_too_late.gd

@@ -1,5 +0,0 @@
-extends Object
-@uid("uid://c4ckv3ryprcn4")
-
-func test():
-    pass

modules/gdscript/tests/scripts/parser/errors/uid_too_late.out

@@ -1,2 +0,0 @@
-GDTEST_PARSER_ERROR
-Annotation "@uid" must be at the top of the script, before "extends" and "class_name".

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

@@ -1,5 +0,0 @@
-@uid("uid://c4ckv3ryprcn4")
-extends Object
-
-func test():
-    pass

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

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