Thread:Manual talk:Skin autodiscovery/Upgrading to 1.23/reply (3)

Two things:

First: As far as old core skins are concerned, Upgrade already tells us to remove these according files and folders as far as these skins have been removed from MediaWiki itself. These files belong to the category "old files left behind, which may cause trouble".

Second: As far as in contrast custom skins are concerned, these should be upgraded as described at Manual:Skin_autodiscovery. You surely can remove them as you described above, but doing so basically just uninstalls the skin. In your case that obviously was OK - for others it may be no option.