samples/subsys/console: Remove unused tx_sem semaphore
samples/subsys/console: Remove unused tx_sem semaphore

This was declared but unused.  And recent toolchains have apparently
started warning on it leading to sanitycheck failures.

Signed-off-by: Andy Ross <c70f9a6bf6ee0cd69c8af4ce5e6b131945769315@intel.com>

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