title: how to remove association in sequelize without extra query?
body: <p>I have many to many association between <code>exercise</code> and <code>muscle</code> models.
  I remove single association </p>
  
  <pre><code>models.Exercise.find({where: {id: exerciseId}})
                  .then(function(exercise){
                      exercise.removeMuscle(muscleId);
                      res.sendStatus(200);
                  });
  </code></pre>
  
  <p>ORM runs 3 queries and 2 of them are similar</p>
  
  <pre><code>Executing (default): SELECT `Muscule`.`id`, `Muscule`.`title`, `Muscule`.`description`, `Muscule`.`video`, `Muscule`.`createdAt`,
      `Muscule`.`updatedAt`, `muscle_exercise`.`createdAt` AS `muscle_exercise.createdAt`, `muscle_exercise`.`updatedAt` AS `muscle_
      exercise.updatedAt`, `muscle_exercise`.`MusculeId` AS `muscle_exercise.MusculeId`, `muscle_exercise`.`ExerciseId` AS `muscle_exercise.ExerciseId` FROM `Muscules` AS `Muscule` INNER JOIN `muscle_exercise` AS `muscle_exercise` ON `Muscule`.`id` = `muscle_exercise`.`MusculeId` AND `muscle_exercise`.`ExerciseId` = 11;
  
  
  
   Executing (default): SELECT `Muscule`.`id`, `Muscule`.`title`, `Muscule`.`description`, `Muscule`.`video`, `Muscule`.`createdAt`,
      `Muscule`.`updatedAt`, `muscle_exercise`.`createdAt` AS `muscle_exercise.createdAt`, `muscle_exercise`.`updatedAt` AS `muscle_
      exercise.updatedAt`, `muscle_exercise`.`MusculeId` AS `muscle_exercise.MusculeId`, `muscle_exercise`.`ExerciseId` AS `muscle_exercise.ExerciseId` FROM `Muscules` AS `Muscule` INNER JOIN `muscle_exercise` AS `muscle_exercise` ON `Muscule`.`id` = `muscle_exercise`.`MusculeId` AND `muscle_exercise`.`ExerciseId` = 11;
  
  
      Executing (default): DELETE FROM `muscle_exercise` WHERE `ExerciseId` = 11 AND `MusculeId` IN (52)
  </code></pre>
  
  <p>Is there any way to avoid duplicate query? And it would be perfect if I can escape first and second query and run only third one that actually do something useful?</p>