Always Call av_probe_input_format

Fortunately, the FFmpeg package in Ubuntu 20.04 also has the `av_probe_input_format` method. Therefore, we can remove the old code.

src/CoreAudio/AFAVFormatComponent/AudioFileFormatGeneric.cpp

@@ -92,15 +92,7 @@ UncertainResult AudioFileFormatGeneric::FileDataIsThisFormat(UInt32 inDataByteSi
 	probeData.buf = buf.data();
 	probeData.buf_size = inDataByteSize;
 
-#warning "TODO: Remove old `read_probe` call once we no longer support older distros" 
-#if LIBAVCODEC_VERSION_MAJOR >= 61
 	return av_probe_input_format(&probeData, false) != nullptr ? kTrue : kFalse;
-#else
-	const AVInputFormat* fmt = av_find_input_format(m_avformatShortName);
-	if (!fmt)
-		return false;
-	return fmt->read_probe(&probeData) ? kTrue : kFalse;
-#endif
 }
 
 AudioFileObject* AudioFileFormatGeneric::New()