fileUtils: remove unused method 'isStaleHandle'

Change-Id: Ie183280861a1f268fc1faa244db3b2cc2dddbb97
Signed-off-by: Yeela Kaplan <ykaplan@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/27180
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>