EffectSelectDialog: sort effect keys instead of plugin names

Commit 360bfe5089c9fd13847b9b982011305fd63daf3f broke mapping between
displayed and internal effect list. Fix this by sorting the effect key
list itself.
Removed old ladspa_effect directory

Something went wrong with the rename in 9c9372f0c87f6d3e6d5b0de3e5509.