[wayland] Drop threaded eglInitialize hack

The hack to perform the first eglInitialize in a thread is no longer
needed, as our internal QPA plugin is either able to share the
EGLDisplay or performs the potentially blocking eglInitialize in a
thread.

main_wayland.cpp

@@ -201,16 +201,6 @@ void ApplicationWayland::continueStartupWithX()
         }
     }
 
-    // HACK: create a QWindow in a thread to force QtWayland to create the client buffer integration
-    // this performs an eglInitialize which would block as it does a roundtrip to the Wayland server
-    // in the main thread. By moving into a thread we get the initialize without hitting the problem
-    // This needs to be done before creating the Workspace as from inside Workspace the dangerous code
-    // gets hit in the main thread
-    QFutureWatcher<void> *eglInitWatcher = new QFutureWatcher<void>(this);
-    connect(eglInitWatcher, &QFutureWatcher<void>::finished, this,
-        [this, eglInitWatcher] {
-            eglInitWatcher->deleteLater();
-
     createWorkspace();
 
     Xcb::sync(); // Trigger possible errors, there's still a chance to abort
@@ -218,13 +208,6 @@ void ApplicationWayland::continueStartupWithX()
     notifyKSplash();
     waylandServer()->createDummyQtWindow();
 }
-    );
-    eglInitWatcher->setFuture(QtConcurrent::run([] {
-        QWindow w;
-        w.setSurfaceType(QSurface::RasterGLSurface);
-        w.create();
-    }));
-}
 
 void ApplicationWayland::createX11Connection()
 {