Remove unused is_marker method from utils.

Change-Id: I67f695b57405465c7bec22c437c2169403fa59dd
Signed-off-by: Peter Portante <peter.portante@redhat.com>
Reviewed-on: http://review.gluster.org/5089
Reviewed-by: Mohammed Junaid <junaid@redhat.com>
Tested-by: Mohammed Junaid <junaid@redhat.com>
Reviewed-by: Luis Pabon <lpabon@redhat.com>