Windows: Multisampling is disabled by default.

The previous code assumed that -1 indicated some sort of "auto",
but this is not the case according to documentation.

Task-number: QTBUG-27600
Change-Id: Id17ce32f94ded61a63a33d0c04ec5312f53c7923
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>

src/plugins/platforms/windows/qwindowsglcontext.cpp

@@ -439,7 +439,7 @@ static int choosePixelFormat(HDC hdc,
         iAttributes[i++] = WGL_SAMPLES_ARB;
         samplesValuePosition = i;
         iAttributes[i++] = format.samples();
-    } else if (samples == 0 || samples == 1 ) {
+    } else {
         iAttributes[i++] = WGL_SAMPLE_BUFFERS_ARB;
         iAttributes[i++] = FALSE;
     }