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/test/RTPFile.cc

@@ -20,10 +20,10 @@
 #endif
 
 #include "audio_coding_module.h"
-#include "webrtc/engine_configurations.h"
 #include "webrtc/system_wrappers/include/rw_lock_wrapper.h"
 // TODO(tlegrand): Consider removing usage of gtest.
 #include "webrtc/test/gtest.h"
+#include "webrtc/voice_engine_configurations.h"
 
 namespace webrtc {