delete check_output backport: Python 2.6 no longer supported

integrations/git/post-receive

@@ -49,21 +49,6 @@ client = zulip.Client(
     api_key=config.ZULIP_API_KEY,
     client="ZulipGit/" + VERSION)
 
-# check_output is backported from subprocess.py in Python 2.7
-def check_output(*popenargs, **kwargs):
-    if 'stdout' in kwargs:
-        raise ValueError('stdout argument not allowed, it will be overridden.')
-    process = subprocess.Popen(stdout=subprocess.PIPE, *popenargs, **kwargs)
-    output, unused_err = process.communicate()
-    retcode = process.poll()
-    if retcode:
-        cmd = kwargs.get("args")
-        if cmd is None:
-            cmd = popenargs[0]
-        raise subprocess.CalledProcessError(retcode, cmd, output=output)
-    return output
-subprocess.check_output = check_output
-
 def git_repository_name():
     output = subprocess.check_output(["git", "rev-parse", "--is-bare-repository"])
     if output.strip() == "true":