core: Clean up RemoveStoragePool.canDoAction

General Java cleanup to RemoveStorageDomain.canDoAction() - moved action
type setting to setActionMessageParameters(), used getXXXDao() methods
where available and removed redundant null check.

Change-Id: I8aa157b7589b3ae5039c71ca07c3dc11ff88ce0d
Signed-off-by: Allon Mureinik <amureini@redhat.com>