Removed everything we don't need from the actual library, and provide
dummy implementations of the main entry points:

  - int32_t WelsCreateSVCEncoder (ISVCEncoder**)
  - void WelsDestroySVCEncoder (ISVCEncoder*)
  - OpenH264Version WelsGetCodecVersion()
  - void WelsGetCodecVersionEx (OpenH264Version* pVersion)
  - int WelsGetDecoderCapability (SDecoderCapability*)
  - long WelsCreateDecoder (ISVCDecoder**)
  - void WelsDestroyDecoder (ISVCDecoder*)

https://phabricator.endlessm.com/T23345