StudioWelcome: Remove cluster tutorial videos

Those videos are outdated.
Also removing the thumbnails.

Change-Id: I07e3215db8a47d9f2e8b28f187b529b81630a4dd
Reviewed-by: Brook Cronin <brook.cronin@qt.io>
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/studiowelcome/qml/welcomepage/TutorialsModel.qml

@@ -26,36 +26,6 @@
 import QtQuick 2.0
 
 ListModel {
-    ListElement {
-        displayName: "Learn to use Qt Design Studio (Part 1)"
-        thumbnail: "images/tutorial1.png"
-        url: "https://www.youtube.com/watch?v=aV6kFxH3Xws"
-    }
-
-    ListElement {
-        displayName: "Learn to use Qt Design Studio (Part 2)"
-        thumbnail: "images/tutorial2.png"
-        url: "https://www.youtube.com/watch?v=Z3uPoe-4UAw"
-    }
-
-    ListElement {
-        displayName: "Learn to use Qt Design Studio (Part 3)"
-        thumbnail: "images/tutorial3.png"
-        url: "https://www.youtube.com/watch?v=9AjvxoeqAKo"
-    }
-
-    ListElement {
-        displayName: "Learn to use Qt Design Studio (Part 4)"
-        thumbnail: "images/tutorial4.png"
-        url: "https://www.youtube.com/watch?v=8pJpdMwLaAg"
-    }
-
-    ListElement {
-        displayName: "Learn to use Qt Design Studio (Part 5)"
-        thumbnail: "images/tutorial5.png"
-        url: "https://www.youtube.com/watch?v=U91nAFReAoU"
-    }
-
     ListElement {
         displayName: "The Designer Tool Developers Love"
         thumbnail: "images/webinar1.png"