HID: nintendo: Remove some unused functions

These functions are defined in the hid-nintendo.c file, but not called
elsewhere, so delete these unused functions.

drivers/hid/hid-nintendo.c:670:20: warning: unused function 'joycon_device_is_left_joycon'.
drivers/hid/hid-nintendo.c:674:20: warning: unused function 'joycon_device_is_right_joycon'

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Closes: https://bugzilla.openanolis.cn/show_bug.cgi?id=7992


Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Reviewed-by: Silvan Jegen <s.jegen@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>