skins2: remove a fallback when choosing a video control

This fallback was an attempt to recover when a skin is poorly designed,
but it causes problems under some circumstances. So let's remove it !

(cherry picked from commit 1d2608d4aa0aa9fe30b9fde5a825f14a9941347c)
Signed-off-by: Erwan Tulou <erwan10@videolan.org>

modules/gui/skins2/src/vout_manager.cpp

@@ -182,15 +182,6 @@ CtrlVideo* VoutManager::getBestCtrlVideo( )
         }
     }
 
-    // as a fallback, look up any video control that is unused
-    for( it = m_pCtrlVideoVec.begin(); it != m_pCtrlVideoVec.end(); ++it )
-    {
-        if( !(*it)->isUsed() )
-        {
-            return (*it);
-        }
-    }
-
     return NULL;
 }