remove "deprecated-declarations" warnings

[juanvallejo]

Before

$ go build examples/transcoder.go
# github.com/imkira/go-libav/avcodec
avcodec/avcodec.go: In function ‘_cgo_a038601aec5c_Cfunc_av_bitstream_filter_close’:
avcodec/avcodec.go:162:2: warning: ‘av_bitstream_filter_close’ is deprecated [-Wdeprecated-declarations]
  FlagLowDelay      Flags = C.CODEC_FLAG_LOW_DELAY
  ^~~~~~~~~~~~~~~~~~~~~~~~~
In file included from avcodec/avcodec.go:4:0:
/usr/include/ffmpeg/libavcodec/avcodec.h:5836:6: note: declared here
 void av_bitstream_filter_close(AVBitStreamFilterContext *bsf);
      ^~~~~~~~~~~~~~~~~~~~~~~~~

...

After

$ go build examples/transcoder.go
$

[codecov-io]

Codecov Report

Merging #42 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #42   +/-   ##
=======================================
  Coverage   33.72%   33.72%           
=======================================
  Files           5        5           
  Lines        2583     2583           
=======================================
  Hits          871      871           
  Misses       1664     1664           
  Partials       48       48

Impacted Files	Coverage Δ
avutil/avutil.go	32.91% <ø> (ø)	⬆️
avcodec/avcodec.go	22.7% <ø> (ø)	⬆️
avfilter/avfilter.go	24.83% <ø> (ø)	⬆️
avformat/avformat.go	56.19% <ø> (ø)	⬆️

---

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[imkira]

@juanvallejo Hi there. Thanks for the contribution. I was thinking, maybe it would be better to get rid of the deprecation itself, rather than just disabling the warning.

[juanvallejo]

@imkira sure, will work on this once I have a bit of time

[imkira]

Thanks @juanvallejo . Please let us know too which version of ffmpeg are you using.