Remove deprecared/unneeded avcodec_close()

[Pleune]

From docs see that this function call is not needed:

"Do not use this function. Use avcodec_free_context() to destroy a codec context (either open or closed). Opening and closing a codec context multiple times is not supported anymore – use multiple codec contexts instead."

avcodec_free_context is already called.

Fixes error: ‘int avcodec_close(AVCodecContext*)’ is deprecated [-Werror=deprecated-declarations] for my builds.