drop old git_require checks

We've been requiring git-1.7.2 since Oct 2012, so we can safely drop
the individual checks sprinkled throughout the code base for older.

Change-Id: I1737fff7b3f27f475960b0bff9cb300aefd5d108
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/253135
Reviewed-by: David Pursehouse <dpursehouse@collab.net>
Tested-by: Mike Frysinger <vapier@google.com>

project.py

@@ -3125,9 +3125,6 @@ class Project(object):
           raise TypeError('%s() got an unexpected keyword argument %r'
                           % (name, k))
         if config is not None:
-          if not git_require((1, 7, 2)):
-            raise ValueError('cannot set config on command line for %s()'
-                             % name)
           for k, v in config.items():
             cmdv.append('-c')
             cmdv.append('%s=%s' % (k, v))