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/modules/audio_coding/codecs/ilbc/encode.c b/modules/audio_coding/codecs/ilbc/encode.c
index fa4ffd0..7254355 100644
--- a/modules/audio_coding/codecs/ilbc/encode.c
+++ b/modules/audio_coding/codecs/ilbc/encode.c
@@ -29,7 +29,7 @@
 #include "index_conv_enc.h"
 #include "pack_bits.h"
 #include "hp_input.h"
-#include "webrtc/rtc_base/checks.h"
+#include "rtc_base/checks.h"
 
 #ifdef SPLIT_10MS
 #include "unpack_bits.h"