Fixing WebRTC after moving from src/webrtc to src/

In https://webrtc-review.googlesource.com/c/src/+/1560 we moved WebRTC
from src/webrtc to src/ (in order to preserve an healthy git history).
This CL takes care of fixing header guards, #include paths, etc...

NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
TBR=tommi@webrtc.org


Bug: chromium:611808
Change-Id: Iea91618212bee0af16aa3f05071eab8f93706578
Reviewed-on: https://webrtc-review.googlesource.com/1561
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Henrik Kjellander <kjellander@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#19846}
diff --git a/api/rtpreceiverinterface.h b/api/rtpreceiverinterface.h
index 3119fb7..afb737b 100644
--- a/api/rtpreceiverinterface.h
+++ b/api/rtpreceiverinterface.h
@@ -11,18 +11,18 @@
 // This file contains interfaces for RtpReceivers
 // http://w3c.github.io/webrtc-pc/#rtcrtpreceiver-interface
 
-#ifndef WEBRTC_API_RTPRECEIVERINTERFACE_H_
-#define WEBRTC_API_RTPRECEIVERINTERFACE_H_
+#ifndef API_RTPRECEIVERINTERFACE_H_
+#define API_RTPRECEIVERINTERFACE_H_
 
 #include <string>
 #include <vector>
 
-#include "webrtc/api/mediastreaminterface.h"
-#include "webrtc/api/mediatypes.h"
-#include "webrtc/api/proxy.h"
-#include "webrtc/api/rtpparameters.h"
-#include "webrtc/rtc_base/refcount.h"
-#include "webrtc/rtc_base/scoped_ref_ptr.h"
+#include "api/mediastreaminterface.h"
+#include "api/mediatypes.h"
+#include "api/proxy.h"
+#include "api/rtpparameters.h"
+#include "rtc_base/refcount.h"
+#include "rtc_base/scoped_ref_ptr.h"
 
 namespace webrtc {
 
@@ -140,4 +140,4 @@
 
 }  // namespace webrtc
 
-#endif  // WEBRTC_API_RTPRECEIVERINTERFACE_H_
+#endif  // API_RTPRECEIVERINTERFACE_H_