utils: fix flake8 warning

Commit 40bb37bd70d refactored get-developers, and now the 'os' module is
no longer needed, but still imported:

    utils/get-developers:6:1: F401 'os' imported but unused
    1     F401 'os' imported but unused

Drop it now.

Reported-by: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit 9277978e28479449e517152105ae2e8a6d03151a)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

utils/get-developers

@@ -3,7 +3,6 @@
 import argparse
 import getdeveloperlib
 import sys
-import os
 
 
 def parse_args():