Bug 1681043 - P6. Remove no longer necessary workaround. r=alwu,bryce

The WMFDecoderModule now uses a crash guard around the loading of the VP9/VP8 MFT. We don't want to always assume that we have a VPx decoder in the GPU process in particular, as it will only be true if a HW decoder is available.

Differential Revision: https://phabricator.services.mozilla.com/D100309

dom/media/platforms/PDMFactory.cpp

@@ -390,15 +390,6 @@ bool PDMFactory::Supports(const SupportDecoderParams& aParams,
   if (mEMEPDM) {
     return mEMEPDM->Supports(aParams, aDiagnostics);
   }
-  if (VPXDecoder::IsVPX(aParams.MimeType(),
-                        VPXDecoder::VP8 | VPXDecoder::VP9) &&
-      !aParams.mConfig.GetAsVideoInfo()->HasAlpha()) {
-    // Work around bug 1521370, where trying to instantiate an external decoder
-    // could cause a crash.
-    // We always ship a VP8/VP9 decoder (libvpx) and optionally we have ffvpx.
-    // So we can speed up the test by assuming that this codec is supported.
-    return true;
-  }
 
   RefPtr<PlatformDecoderModule> current =
       GetDecoderModule(aParams, aDiagnostics);