extract id from clients array

schema.js

clientSchema.pre('remove', function(next) {

  // clean up dependencies
	Sweepstakes.remove({client_id: this._id}).exec();
	Submission.remove({client_id: this._id}).exec();

	// remove client id from users
	User.update({clients: {$in: [this._id]}}, {$pull: {clients: this._id}}, function(err, numAffected) {
	   	
	   	if (err)
	   		console.log(err);

	   	console.log('NUMBER OF ROWS AFFECTED: ', numAffected);

	    next();

	});

});