Use COPY_STATEID to copy stateid.

Removed an unused call to state_share_check_conflict(), used
COPY_STATEID to copy delegation stateid.

Signed-off-by: Malahal Naineni <malahal@us.ibm.com>
Clean up in nfs4_op_delegreturn

Signed-off-by: Malahal Naineni <malahal@us.ibm.com>
Fix subtract_deleg_from_list.

Also renamed the function to remove_deleg_lock. Also added missing owner
ref decrement when we free the delegation.

Signed-off-by: Malahal Naineni <malahal@us.ibm.com>