js: Use templates for non-translatable strings

This reverts commit 9d941f8202 and replaces all additional
instances of .format() that have been added since.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2160>

js/ui/background.js

@@ -271,7 +271,7 @@ var Background = GObject.registerClass({
             this._settings.connect('changed', this._emitChangedSignal.bind(this));
 
         this._colorSchemeChangedSignalId =
-            this._interfaceSettings.connect('changed::%s'.format(COLOR_SCHEME_KEY),
+            this._interfaceSettings.connect(`changed::${COLOR_SCHEME_KEY}`,
                 this._emitChangedSignal.bind(this));
 
         this._load();