logging: Fix string stripping Kconfig option dependency

Change to depend on LOG_DICTIONARY_DB which is broader than
LOG_DICTIONARY_SUPPORT which is set only when log_output
supports dictionary mode. However, it is possible that
log_output is not used when dictionary mode is used. Database
generation is always enabled when dictionary mode is used.

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>