avutil/pixdesc: remove reference to avcodec_get_chroma_sub_sample

Don't recommend to use deprecated functions.
Signed-off-by: James Almer <jamrial@gmail.com>

libavutil/pixdesc.h

@@ -225,11 +225,6 @@ enum AVPixelFormat av_pix_fmt_desc_get_id(const AVPixFmtDescriptor *desc);
  * Utility function to access log2_chroma_w log2_chroma_h from
  * the pixel format AVPixFmtDescriptor.
  *
- * See av_get_chroma_sub_sample() for a function that asserts a
- * valid pixel format instead of returning an error code.
- * Its recommended that you use avcodec_get_chroma_sub_sample unless
- * you do check the return code!
- *
  * @param[in]  pix_fmt the pixel format
  * @param[out] h_shift store log2_chroma_w (horizontal/width shift)
  * @param[out] v_shift store log2_chroma_h (vertical/height shift)