Revert r7798 ("Move the AudioDecoder interface out of NetEq")

Apparently, it caused all sorts of problems I don't have time to
straighten out right now.

TBR=henrika@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/25289004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7799 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/webrtc/modules/audio_coding/neteq/decoder_database.h b/webrtc/modules/audio_coding/neteq/decoder_database.h
index cae1021..8a03f21 100644
--- a/webrtc/modules/audio_coding/neteq/decoder_database.h
+++ b/webrtc/modules/audio_coding/neteq/decoder_database.h
@@ -15,12 +15,15 @@
 
 #include "webrtc/base/constructormagic.h"
 #include "webrtc/common_types.h"  // NULL
-#include "webrtc/modules/audio_coding/neteq/audio_decoder_impl.h"
+#include "webrtc/modules/audio_coding/neteq/interface/audio_decoder.h"
 #include "webrtc/modules/audio_coding/neteq/packet.h"
 #include "webrtc/typedefs.h"
 
 namespace webrtc {
 
+// Forward declaration.
+class AudioDecoder;
+
 class DecoderDatabase {
  public:
   enum DatabaseReturnCodes {