Changelog: remove av_{base,dir}_name addition.

This belongs only to APIChanges, where it is already present.

Spotted-by: Stefano

Changelog

@@ -50,7 +50,6 @@ version <next>:
 - documentation split into per-component manuals
 - pp (postproc) filter ported from MPlayer
 - NIST Sphere demuxer
-- av_basename and av_dirname
 - MPL2, VPlayer, MPlayer, AQTitle, PJS and SubViewer v1 subtitles demuxers and decoders