Test all renderers before use

Every renderer except SDL had opted-in for testing due to various
quirks discovered over the years, so just do away with this option
and test all renderers.

app/streaming/video/ffmpeg-renderers/plvk.cpp

@@ -1021,12 +1021,6 @@ int PlVkRenderer::getDecoderCapabilities()
            CAPABILITY_REFERENCE_FRAME_INVALIDATION_AV1;
 }
 
-bool PlVkRenderer::needsTestFrame()
-{
-    // We need a test frame to verify that Vulkan video decoding is working
-    return true;
-}
-
 bool PlVkRenderer::isPixelFormatSupported(int videoFormat, AVPixelFormat pixelFormat)
 {
     if (m_HwAccelBackend) {