staging: rtl8192u: Remove function dm_backup_dynamic_mechanism_state()

Remove unused function dm_backup_dynamic_mechanism_state.
Issue found with Coccinelle.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>