Remove part of the mergeField comment (#822)

Author: schmidt-sebastian

packages/firebase/index.d.ts

@@ -1179,9 +1179,6 @@ declare namespace firebase.firestore {
      * Changes the behavior of set() calls to only replace the specified field
      * paths. Any field path that is not specified is ignored and remains
      * untouched.
-     *
-     * <p>It is an error to pass a SetOptions object to a set() call that is
-     * missing a value for any of the fields specified here.
      */
     readonly mergeFields?: (string | FieldPath)[];
   }

packages/firestore-types/index.d.ts

@@ -498,9 +498,6 @@ export interface SetOptions {
    * Changes the behavior of set() calls to only replace the specified field
    * paths. Any field path that is not specified is ignored and remains
    * untouched.
-   *
-   * <p>It is an error to pass a SetOptions object to a set() call that is
-   * missing a value for any of the fields specified here.
    */
   readonly mergeFields?: (string | FieldPath)[];
 }