This commit removes obsolete statefulset create, delete,
addlabel, templateToStatefulset functions which were part of
deprecated csi support for k8s 1.13 and should have been
removed as part of https://github.com/rook/rook/pull/5982.
It also adds Unit test for templateToDeployment func.
Signed-off-by: Rakshith R <rar@redhat.com>