platform/x86: surface3_power: Drop unused structure definition

As reported by kbuild bot the struct mshw0011_lookup in never used.
Drop its definition for good.

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/platform/x86/surface3_power.c

@@ -56,13 +56,6 @@ struct mshw0011_data {
 	s32			full_capacity;
 };
 
-struct mshw0011_lookup {
-	struct mshw0011_data	*cdata;
-	unsigned int		n;
-	unsigned int		index;
-	int			addr;
-};
-
 struct mshw0011_handler_data {
 	struct acpi_connection_info	info;
 	struct i2c_client		*client;