Issue-2750 - Remove log pollution
Issue-2750 - Remove log pollution

Add empty skill directories to a set and remove them whenever they are
no longer empty. Empty skill directories only appear once in the log.

==== Fixed Issues ====
log polution - #2750

MycroftAI/mycroft-core,MycroftAI/mycroft-core,forslund/mycroft-core,forslund/mycroft-core