net: l2: ppp: drop unused PPP_TIMEOUT macro
net: l2: ppp: drop unused PPP_TIMEOUT macro

This macro has no use in code and was most probably replaced by
FSM_TIMEOUT (which resolves to CONFIG_NET_L2_PPP_TIMEOUT) with the same
default value.

Signed-off-by: Marcin Niestroj <63506c06cfbc47ace147db1702f6e751f5ac2132@grinn-global.com>

Vudentz/zephyr,Vudentz/zephyr,galak/zephyr,nashif/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,Vudentz/zephyr,Vudentz/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,nashif/zephyr,finikorg/zephyr,nashif/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr