extcon: realtek: Remove unused of_gpio.h

of_gpio.h is deprecated and subject to remove.
The driver doesn't use it, simply remove the unused header.

Link: https://lore.kernel.org/lkml/20240304174913.1198974-1-andriy.shevchenko@linux.intel.com/


Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>