appDisplay: Open new window on middle-click

The current middle-click action of opening a new window on a new
workspace is a bit peculiar; it is also not overly hard to achieve
the same result by moving a new window to the desired workspace or
selecting a workspace before opening a new window. Just opening
a new window is also a more common action, so having a shortcut
available that doesn't require a modifier is a good idea as well;
change the middle-click behavior accordingly.

https://bugzilla.gnome.org/show_bug.cgi?id=695010

js/ui/appDisplay.js

@@ -1388,9 +1388,6 @@ const AppIcon = new Lang.Class({
         if (button == 1) {
             this._onActivate(Clutter.get_current_event());
         } else if (button == 2) {
-            // Last workspace is always empty
-            let launchWorkspace = global.screen.get_workspace_by_index(global.screen.n_workspaces - 1);
-            launchWorkspace.activate(global.get_current_time());
             this.app.open_new_window(-1);
             Main.overview.hide();
         }