Fix flake8 issue

gfx_critical_errors.py

@@ -3,7 +3,6 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this file,
 # You can obtain one at http://mozilla.org/MPL/2.0/.
 
-import argparse
 import re
 import requests
 import libmozdata.utils as utils