removing _make_directory_locked function

This function was added as a workaround for race condition
bug found in earlier versions of Glusterfs. The bug has since
been fixed in the latest version of Glusterfs, so there's no
need to support this code any longer.

Change-Id: I50ebb66bdf0553ae8bab98ed8f783e0389e83fa8
Signed-off-by: Thiago da Silva <thiago@redhat.com>
Reviewed-on: http://review.gluster.org/7335
Reviewed-by: Luis Pabon <lpabon@redhat.com>
Tested-by: Luis Pabon <lpabon@redhat.com>