RemoveMobileUnfriendlyPlugins: unregister all MobileUnfriendly plugins

see: http://vanillaforums.org/discussion/comment/216131/#Comment_216131

PluginManager->UnRegisterPlugin() unregisters by classname, but the
classname isn't always PluginName + 'Plugin'

This causes plugins not to be removed on mobile, regardless of what the
PluginInfo says about mobile-friendlyness.

This PR fixes that.