Remove unused methods
Remove unused methods

Manila doesn't use methods ensure_tree and delete_if_exists anywhere,
and oslo.utils provides same methods in module fileutils. We can use
them from oslo.utils if we need in the futrue.

TrivialFix

Change-Id: I280b674dca3738d26c2bed2cf71e94775b370cd5

NetApp/manila,openstack/manila,vponomaryov/manila,NetApp/manila,vponomaryov/manila,bswartz/manila,bswartz/manila,openstack/manila