gdb: fix flake-7.2.0 F824 warning

This patch fixes the flake8 warning F824 [1]:

| F824 `global gtype_cache` is unused: name is never assigned in scope

This patch removes the `global` definition inside the function since,
according to [2], it's already considered global.

[1]: https://flake8.pycqa.org/en/latest/user/error-codes.html
[2]: https://docs.python.org/3/faq/programming.html#what-are-the-rules-for-local-and-global-variables-in-python

Reviewed-by: Sergey Bronnikov <[email protected]>
Signed-off-by: Sergey Kaplun <[email protected]>

Author: Buristan

src/luajit-gdb.py

@@ -23,7 +23,6 @@
 
 
 def gtype(typestr):
-    global gtype_cache
     if typestr in gtype_cache:
         return gtype_cache[typestr]