use sources.master.min_count_tags to set min_tag_combination_count in tagstats_handler.hpp

use sources.master.min_count_tags to set min_tag_combination_count in tagstats_handler.hpp

Follow up to 68d4a9c .  This should remove the last case where code needs to be changed for regional deployments.

master.min_count_tag   should probably be renamed to min_tag_combination_count, but I kept changes to the minimum