remove_vertex_from_inactive_vertex_groups.py

import bpy

class OBJECT_OT_vertex_group_remove_from_inactive(bpy.types.Operator):
    """Remove selected vertices from inactive vertex groups"""
    bl_idname = "object.vertex_group_remove_from_inactive"
    bl_label = "Remove Vertex From Inactive Vertex Groups"
    bl_options = {'REGISTER', 'UNDO'}

    @classmethod
    def poll(cls, context):
        obj = context.active_object
        return (obj and 
                obj.type == "MESH" and
                obj.vertex_groups)

    def execute(self, context):
        obj = context.active_object
        #removing vertices from vertex groups
        #requires object mode
        mode = obj.mode
        if not mode == "OBJECT":
            bpy.ops.object.mode_set(mode="OBJECT")
        
        active = obj.vertex_groups.active_index
        selection = [v.index for v in obj.data.vertices if v.select]
        
        for group in obj.vertex_groups:
            if group.index == active:
                continue
            group.remove(selection)
        
        if not mode == "OBJECT":
            bpy.ops.object.mode_set(mode=mode)
        return {'FINISHED'}

def draw_op(self, layout):
    self.layout.column().operator("object.vertex_group_remove_from_inactive")

def register():
    bpy.utils.register_class(OBJECT_OT_vertex_group_remove_from_inactive)
    bpy.types.VIEW3D_PT_tools_meshweight.append(draw_op)

def unregister():
    bpy.types.VIEW3D_PT_tools_meshweight.remove(draw_op)
    bpy.utils.unregister_class(OBJECT_OT_vertex_group_remove_from_inactive)
    
if __name__ == "__main__":
    register()