staging: r8188eu: remove interrupt_handler from struct hal_ops

Remove interrupt_handler 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/20210906010106.898-9-phil@philpotter.co.ukSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/r8188eu/include/hal_intf.h

@@ -149,8 +149,6 @@ struct hal_ops {
 	void	(*dm_init)(struct adapter *padapter);
 	void	(*dm_deinit)(struct adapter *padapter);
 
-	s32	(*interrupt_handler)(struct adapter *padapter);
-
 	void	(*set_bwmode_handler)(struct adapter *padapter,
 				      enum ht_channel_width Bandwidth,
 				      u8 Offset);