core: remove outdated comment (#2868)

Fixes: https://github.com/transloadit/uppy/issues/2787

packages/@uppy/core/src/index.js

@@ -705,8 +705,6 @@ class Uppy {
   /**
    * Add multiple files to `state.files`. See the `addFile()` documentation.
    *
-   * This cuts some corners for performance, so should typically only be used in cases where there may be a lot of files.
-   *
    * If an error occurs while adding a file, it is logged and the user is notified. This is good for UI plugins, but not for programmatic use. Programmatic users should usually still use `addFile()` on individual files.
    */
   addFiles (fileDescriptors) {