samples: subsys: debug: Remove CONFIG_SEGGER_RTT assignment
samples: subsys: debug: Remove CONFIG_SEGGER_RTT assignment

This symbol does not exist. Not sure what was intended.

There's HAS_SEGER_RTT, but that symbol has no prompt, meaning .config
values have no effect on it. It is 'select'ed by the SoCs.

Remove the assignment, which is a no-op.

Signed-off-by: Ulf Magnusson <01743f1c1deb1fe75271d62edb65757d98ac0bcb@nordicsemi.no>

zephyriot/zephyr,nashif/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,finikorg/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,ldts/zephyr,kraj/zephyr,Vudentz/zephyr,mbolivar/zephyr,kraj/zephyr,galak/zephyr,punitvara/zephyr,finikorg/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,ldts/zephyr,zephyriot/zephyr,ldts/zephyr,zephyriot/zephyr,ldts/zephyr,Vudentz/zephyr,punitvara/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,nashif/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,mbolivar/zephyr,explora26/zephyr,nashif/zephyr,kraj/zephyr,finikorg/zephyr,punitvara/zephyr,zephyriot/zephyr,zephyrproject-rtos/zephyr,kraj/zephyr,explora26/zephyr,galak/zephyr,galak/zephyr,mbolivar/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,Vudentz/zephyr,galak/zephyr,explora26/zephyr,kraj/zephyr,mbolivar/zephyr,mbolivar/zephyr,zephyriot/zephyr,punitvara/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,Vudentz/zephyr