Remove CELT / Opus confusion in labels, doc and comments.

The situation was not clear when support was added but it is now:
CELT and Opus are really two different codecs.
The current code supports CELT via libcelt, not Opus.
Signed-off-by: Nicolas George <nicolas.george@normalesup.org>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

configure

@@ -162,7 +162,7 @@ Configuration options:
 External library support:
   --enable-avisynth        enable reading of AVISynth script files [no]
   --enable-bzlib           enable bzlib [autodetect]
-  --enable-libcelt         enable CELT/Opus decoding via libcelt [no]
+  --enable-libcelt         enable CELT decoding via libcelt [no]
   --enable-frei0r          enable frei0r video filtering
   --enable-libaacplus      enable AAC+ encoding via libaacplus [no]
   --enable-libopencore-amrnb enable AMR-NB de/encoding via libopencore-amrnb [no]

doc/general.texi

@@ -619,7 +619,7 @@ following image formats are supported:
 @item Atrac 3                @tab     @tab  X
 @item Bink Audio             @tab     @tab  X
     @tab Used in Bink and Smacker files in many games.
-@item CELT (Opus)            @tab     @tab  E
+@item CELT                   @tab     @tab  E
     @tab decoding supported through external library libcelt
 @item Delphine Software International CIN audio  @tab     @tab  X
     @tab Codec used in Delphine Software International games.

libavcodec/libcelt_dec.c

 /*
- * Xiph CELT / Opus decoder using libcelt
+ * Xiph CELT decoder using libcelt
  * Copyright (c) 2011 Nicolas George
  *
  * This file is part of FFmpeg.
@@ -133,5 +133,5 @@ AVCodec ff_libcelt_decoder = {
     .close          = libcelt_dec_close,
     .decode         = libcelt_dec_decode,
     .capabilities   = 0,
-    .long_name = NULL_IF_CONFIG_SMALL("Xiph CELT/Opus decoder using libcelt"),
+    .long_name      = NULL_IF_CONFIG_SMALL("Xiph CELT decoder using libcelt"),
 };

libavformat/oggparsecelt.c

 /*
- * Xiph CELT / Opus parser for Ogg
+ * Xiph CELT parser for Ogg
  * Copyright (c) 2011 Nicolas George
  *
  * This file is part of FFmpeg.