Remove obsolete link to vorbis.com.

There remains a link from the Vorbis RTP format RFC, which is
an immutable published document. We'll have to maintain a
redirect for the sake of that link.

Signed-off-by: Mark Harris <mark.hsj@gmail.com>

README.md

@@ -63,8 +63,6 @@ Vorbis's homepage is located at 'https://www.xiph.org/vorbis/'.
 Up to date technical documents, contact information, source code and
 pre-built utilities may be found there.
 
-The user website for Ogg Vorbis software and audio is http://vorbis.com/
-
 ## Building ##
 
 #### Building from master ####