scripts: Reverted del to resolve shadowed builtins

I don't know how I completely missed that this doesn't actually work!

Using del _does_ work in Python's repl, but it makes sense the repl may
differ from actual function execution in this case.

The problem is Python still thinks the relevant builtin is a local
variables after deletion, raising an UnboundLocalError instead of
performing a global lookup. In theory this would work if the variable
could be made global, but since global/nonlocal statements are lifted,
Python complains with "SyntaxError: name 'list' is parameter and
global".

And that's A-Ok! Intentionally shadowing language builtins already puts
this code deep into ugly hacks territory.

scripts/parity.py

@@ -49,7 +49,8 @@ def parity(x):
 def main(paths, *,
         hex=False,
         string=False):
-    hex_ = hex; del hex
+    import builtins
+    hex_, hex = hex, builtins.hex
 
     # interpret as sequence of hex bytes
     if hex_: