overviewControls: Remove slide transitions before setting value manually

Remove transitions of the `slide-x` property of the layout manager
before we set the property to a fixed value, otherwise the transitions
might still be running and change the value after we set it.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/707

js/ui/overviewControls.js

@@ -248,6 +248,7 @@ var SlidingControl = class {
         // selector; this means we can now safely set the full slide for
         // the next page, since slideIn or slideOut might have been called,
         // changing the visiblity
+        this.actor.remove_transition('@layout.slide-x');
         this.layout.slide_x = this._getSlide();
         this._updateTranslation();
     }