user.belongsToMany(group,{through:"user_group"});
group.belongsToMany(gruseroup,{through:"user_group"}); assume that the user_group table has a record of userId:1,groupId:1. 
 how do I delete this record? 
user.belongsToMany(group,{through:"user_group"});
group.belongsToMany(gruseroup,{through:"user_group"}); assume that the user_group table has a record of userId:1,groupId:1. 
 how do I delete this record?