[gdb] Remove unused import (python#13682)

Unblocks python#13680

Author: srittau

stubs/gdb/gdb/__init__.pyi

@@ -12,7 +12,6 @@ from typing_extensions import TypeAlias, deprecated
 
 import gdb.FrameDecorator
 import gdb.types
-import gdb.xmethod
 
 # The following submodules are automatically imported
 from . import events as events, printing as printing, prompt as prompt, types as types