logging: kconfig: Remove legacy SYS_LOG symbols
logging: kconfig: Remove legacy SYS_LOG symbols

Replaced by the new CONFIG_LOG system.

Also remove the "Logging Options" menu and turn the LOG symbol into a
'menuconfig', with prompt "Logging", which appears in the top menu. LOG
and its dependent symbols make up all of the logging Kconfig symbols
now.

Piggyback some minor cleanup.

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

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