patman: Drop unnecessary import in gitutil

The checkpatch module is not used, so drop it.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reported-by: Stefan Bosch <stefan_b@posteo.net>

tools/patman/gitutil.py

@@ -7,7 +7,6 @@ import os
 import subprocess
 import sys
 
-from patman import checkpatch
 from patman import command
 from patman import series
 from patman import settings