Remove Unused Vertex Groups (Blender addon)
Doing exactly what it says. Can be found trough search or in vertex group menu. in archive 2 versions for 2.7x and 2.8x
Original author: ave
Port to 2.7x: CoDEmanX
Port to 2.8x: Don'tKnow
original page: https://blenderartists.org/t/batch-delete-vertex-groups-script/449881/2