plugins/fadingpopups: Fix autohidden panels blinking when plasmashell launches

The autohidden panels "blink" because this effect animates their opacity.

The dock windows are animated because, as the comment says, the old effect
animated almost every window.

Conceptually, animating docks doesn't align with the purpose of this effect.

src/plugins/fadingpopups/package/contents/code/main.js

@@ -56,7 +56,7 @@ function isPopupWindow(window) {
     // this one. In addition to popups, this effect also animates some
     // special windows(e.g. notifications) because the monolithic version
     // was doing that.
-    if (window.dock || window.splash || window.toolbar
+    if (window.splash || window.toolbar
             || window.notification || window.onScreenDisplay
             || window.criticalNotification
             || window.appletPopup) {