Delete old video defines in engine config.

This CL deletes the old and not used video defines in
engine_configurations.h and pre-pends voice_ to indicate there are only
voice/audio defines left in the file.

BUG=none
R=solenberg@webrtc.org

Review URL: https://codereview.webrtc.org/2401673002 .

Cr-Commit-Position: refs/heads/master@{#14558}

webrtc/modules/audio_coding/neteq/audio_decoder_impl.h

@@ -13,7 +13,6 @@
 
 #include <assert.h>
 
-#include "webrtc/engine_configurations.h"
 #include "webrtc/base/constructormagic.h"
 #include "webrtc/modules/audio_coding/codecs/audio_decoder.h"
 #ifdef WEBRTC_CODEC_G722
@@ -21,6 +20,7 @@
 #endif
 #include "webrtc/modules/audio_coding/acm2/rent_a_codec.h"
 #include "webrtc/typedefs.h"
+#include "webrtc/voice_engine_configurations.h"
 
 namespace webrtc {