Remove unused Python imports

contrib/devtools/github-merge.py

@@ -15,7 +15,7 @@
 # In case of a clean merge that is accepted by the user, the local branch with
 # name $BRANCH is overwritten with the merged result, and optionally pushed.
 from __future__ import division,print_function,unicode_literals
-import os,sys
+import os
 from sys import stdin,stdout,stderr
 import argparse
 import subprocess