Remove always_collect_trace_info from memcached.json

MB-60932 removed the use of always_collect_trace_info in memcached. It was decided to remove the option to disable collection of trace spans as by doing so it becomes hard (read impossible) to figure out why things are slow (where a slow operation spent its time)

always_collect_trace_info is currently accepted as a parameter, but if set to false it will emit a log message (and be ignored). The ask is to remove the setting.