Revert [34013] and parts of [33970].

* `_WP_Editors::wp_mce_translation()` can't be changed without changing strings in TinyMCE and plugins.
* `\u2026` is escaped by `json_encode()` to `\\u2026`, makes `\u2026` visible in our UI.

See #32875.

git-svn-id: https://develop.svn.wordpress.org/trunk@34087 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-customize-manager.php

@@ -627,7 +627,7 @@ final class WP_Customize_Manager {
 			'activeSections' => array(),
 			'activeControls' => array(),
 			'l10n' => array(
-				'loading'  => __( 'Loading\u2026' ),
+				'loading'  => __( 'Loading...' ),
 			),
 		);