doc: fix references to obsolete presets directories for avconv/ffmpeg

cmdutils.h

@@ -334,7 +334,7 @@ int64_t guess_correct_pts(PtsCorrectionContext *ctx, int64_t pts, int64_t dts);
  *
  * If is_path is non-zero, look for the file in the path preset_name.
  * Otherwise search for a file named arg.ffpreset in the directories
- * $FFMPEG_DATADIR (if set), $HOME/.ffmpeg, and in the datadir defined
+ * $AVCONV_DATADIR (if set), $HOME/.avconv, and in the datadir defined
  * at configuration time, in that order. If no such file is found and
  * codec_name is defined, then search for a file named
  * codec_name-preset_name.ffpreset in the above-mentioned directories.

doc/ffmpeg.texi

@@ -806,8 +806,8 @@ preset options identifies the preset file to use according to the
 following rules:
 
 First ffmpeg searches for a file named @var{arg}.ffpreset in the
-directories @file{$FFMPEG_DATADIR} (if set), and @file{$HOME/.ffmpeg}, and in
-the datadir defined at configuration time (usually @file{PREFIX/share/ffmpeg})
+directories @file{$AVCONV_DATADIR} (if set), and @file{$HOME/.avconv}, and in
+the datadir defined at configuration time (usually @file{PREFIX/share/avconv})
 in that order. For example, if the argument is @code{libx264-max}, it will
 search for the file @file{libx264-max.ffpreset}.