'Armature' mode for the Mask Modifier was not working at all anymore even when the selection <-> depsgraph recalc issue was patched to work (this latter fix is coming in another commit). It appears that this probably happened during one or more of the refactors which may have taken place around here over the years since I first introduced it. This commit does two things: * Removed the unused/redundant "vgroupHash" * Fixed the incorrect assumption used for determining if the vertex actually belonged to a vgroup corresponding to a selected bone.