include: remove unused header file gdb_server.h
include: remove unused header file gdb_server.h

A leftover header file from the past.

Signed-off-by: Anas Nashif <0d9952ec84ac43c159f6b7e7ed99a9080c00dd6e@intel.com>

GiulianoFranchetto/zephyr,GiulianoFranchetto/zephyr,GiulianoFranchetto/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,ldts/zephyr,galak/zephyr,ldts/zephyr,Vudentz/zephyr,galak/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,Vudentz/zephyr,explora26/zephyr,Vudentz/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,nashif/zephyr,galak/zephyr,Vudentz/zephyr,Vudentz/zephyr,nashif/zephyr,explora26/zephyr,finikorg/zephyr,finikorg/zephyr