avformat: remove HLS protocol

The use of this protocol was already discouraged and warned about
for years with the recommendation to use the HLS demuxer instead.

doc/protocols.texi

@@ -417,26 +417,6 @@ Gophers protocol.
 
 The Gopher protocol with TLS encapsulation.
 
-@section hls
-
-Read Apple HTTP Live Streaming compliant segmented stream as
-a uniform one. The M3U8 playlists describing the segments can be
-remote HTTP resources or local files, accessed using the standard
-file protocol.
-The nested protocol is declared by specifying
-"+@var{proto}" after the hls URI scheme name, where @var{proto}
-is either "file" or "http".
-
-@example
-hls+http://host/path/to/remote/resource.m3u8
-hls+file://path/to/local/resource.m3u8
-@end example
-
-Using this protocol is discouraged - the hls demuxer should work
-just as well (if not, please report the issues) and is more complete.
-To use the hls demuxer instead, simply use the direct URLs to the
-m3u8 files.
-
 @section http
 
 HTTP (Hyper Text Transfer Protocol).