Revert "Check for existence of refs upon initial fetch"

This reverts commit 565480588d.

We are reverting this change for 2 reasons:

1) It introduced a bug for users using sync -c with a reference mirror.
2) The fetch specs have recently changed to cause git to properly fail
when we request a non-existent branch of a manifest, removing the need
for this change.

Change-Id: I0f63da9bfb40cf5ffafb7979f1b8c929a738fc7b

project.py

@@ -1872,11 +1872,6 @@ class Project(object):
       time.sleep(random.randint(30, 45))
 
     if initial:
-      # Ensure that some refs exist.  Otherwise, we probably aren't looking
-      # at a real git repository and may have a bad url.
-      if not self.bare_ref.all:
-        ok = False
-
       if alt_dir:
         if old_packed != '':
           _lwrite(packed_refs, old_packed)