Revert "When using GIT_OBJECT_DIRECTORY, don't require presence of 'objects' subdirectory"

This reverts commit eb792ea.

Seems to break CI
Related to #1000

Author: Byron

git/repo/fun.py

@@ -35,8 +35,7 @@ def is_git_dir(d):
             There is the unlikely danger to throw if we see directories which just look like a worktree dir,
             but are none."""
     if osp.isdir(d):
-        if (osp.isdir(osp.join(d, 'objects')) or os.environ.has_key('GIT_OBJECT_DIRECTORY')) \
-           and osp.isdir(osp.join(d, 'refs')):
+        if osp.isdir(osp.join(d, 'objects')) and osp.isdir(osp.join(d, 'refs')):
             headref = osp.join(d, 'HEAD')
             return osp.isfile(headref) or \
                 (osp.islink(headref) and