style(model): remove some more jsdoc "callback" references

also combine "always true" paths for "aggregate"

lib/model.js

@@ -2231,7 +2231,7 @@ Model.$where = function $where() {
 /**
  * Issues a mongodb findOneAndUpdate command.
  *
- * Finds a matching document, updates it according to the `update` arg, passing any `options`, and returns the found document (if any) to the callback. The query executes if `callback` is passed else a Query object is returned.
+ * Finds a matching document, updates it according to the `update` arg, passing any `options`. A Query object is returned.
  *
  * #### Example:
  *
@@ -3992,7 +3992,7 @@ function _update(model, op, conditions, doc, options) {
 /**
  * Performs [aggregations](https://www.mongodb.com/docs/manual/aggregation/) on the models collection.
  *
- * If a `callback` is passed, the `aggregate` is executed and a `Promise` is returned. If a callback is not passed, the `aggregate` itself is returned.
+ * The `aggregate` itself is returned.
  *
  * This function triggers the following middleware.
  *
@@ -4047,10 +4047,6 @@ Model.aggregate = function aggregate(pipeline, options) {
     aggregate.option(options);
   }
 
-  if (typeof callback === 'undefined') {
-    return aggregate;
-  }
-
   return aggregate;
 };
 
@@ -4238,7 +4234,6 @@ Model.validate = async function validate(obj, pathsOrOptions, context) {
  * @param {Object} [options.options=null] Additional options like `limit` and `lean`.
  * @param {Function} [options.transform=null] Function that Mongoose will call on every populated document that allows you to transform the populated document.
  * @param {Boolean} [options.forceRepopulate=true] Set to `false` to prevent Mongoose from repopulating paths that are already populated
- * @param {Function} [callback(err,doc)] Optional callback, executed upon completion. Receives `err` and the `doc(s)`.
  * @return {Promise}
  * @api public
  */