Remove webrtc_all target

Move all its configuration to all.gyp instead, which is
not processed by Chromium builds (webrtc.gyp is).

BUG=webrtc:5949
NOTRY=True

Review-Url: https://codereview.webrtc.org/2060873002
Cr-Commit-Position: refs/heads/master@{#13124}
diff --git a/OWNERS b/OWNERS
index 5812db5..6da5c88 100644
--- a/OWNERS
+++ b/OWNERS
@@ -4,8 +4,9 @@
 tina.legrand@webrtc.org
 tommi@webrtc.org
 per-file .gitignore=*
-per-file AUTHORS=*
 per-file .gn=kjellander@webrtc.org
+per-file *.gyp=*
+per-file AUTHORS=*
 per-file BUILD.gn=kjellander@webrtc.org
 per-file DEPS=*
 per-file PRESUBMIT.py=kjellander@webrtc.org