scripts: Adopted del to resolve shadowed builtins

So:

  all_ = all; del all

Instead of:

  import builtins
  all_, all = all, builtins.all

The del exposes the globally scoped builtin we accidentally shadow.

This requires less megic, and no module imports, though tbh I'm
surprised it works.

It also works in the case where you change a builtin globally, but
that's a bit too crazy even for me...

scripts/dbgtag.py

@@ -232,8 +232,7 @@ def main(tags, *,
         block_count=None,
         off=None,
         **args):
-    import builtins
-    list_, list = list, builtins.list
+    list_ = list; del list
 
     # list all known tags
     if list_: