realtek: ZyXEL GS1900-48: drop gpio-restart

realtek: ZyXEL GS1900-48: drop gpio-restart

GPIO 5 on the RTL8231 is defined reset the system, but fails to actually
do so. This triggers a kernel a number of warnings and backtrace for
GPIO pins that can sleep, such as the RTL8231's. Two warnings are
emitted by libgpiod, and a third warning by gpio-restart itself after it
fails to restart the system:

[  106.654008] ------------[ cut here ]------------
[  106.659240] WARNING: CPU: 0 PID: 4279 at drivers/gpio/gpiolib.c:3098 gpiod_set_value+0x7c/0x108
               [ Stack dump and call trace ]
[  106.826218] ---[ end trace d1de50b401f5a153 ]---
[  106.962992] ------------[ cut here ]------------
[  106.968208] WARNING: CPU: 0 PID: 4279 at drivers/gpio/gpiolib.c:3098 gpiod_set_value+0x7c/0x108
               [ Stack dump and call trace ]
[  107.136718] ---[ end trace d1de50b401f5a154 ]---
[  111.087092] ------------[ cut here ]------------
[  111.092271] WARNING: CPU: 0 PID: 4279 at drivers/power/reset/gpio-restart.c:46 gpio_restart_notify+0xc0/0xdc
               [ Stack dump and call trace ]
[  111.256629] ---[ end trace d1de50b401f5a155 ]---

By removing gpio-restart from this device, we skip the restart-by-GPIO
attempt and rely only on the watchdog for restarts, which is already the
de facto behaviour.

Signed-off-by: Sander Vanheule <sander@svanheule.net>