staging: r8188eu: remove enable_interrupt from struct hal_ops

Remove enable_interrupt function pointer from struct hal_ops, as it
is unused.
Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/r/20210906010106.898-5-phil@philpotter.co.ukSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/r8188eu/include/hal_intf.h

@@ -149,7 +149,6 @@ struct hal_ops {
 	void	(*dm_init)(struct adapter *padapter);
 	void	(*dm_deinit)(struct adapter *padapter);
 
-	void	(*enable_interrupt)(struct adapter *padapter);
 	void	(*disable_interrupt)(struct adapter *padapter);
 	s32	(*interrupt_handler)(struct adapter *padapter);