OWNERS: Make everyone able to change *.gn,*.gni files.

Project-wide change to make it possible for all team members
to do changes to GN files.

NOTRY=True
R=kwiberg@webrtc.org
TBR=henrika@webrtc.org

Review URL: https://codereview.webrtc.org/2320043002 .

Cr-Commit-Position: refs/heads/master@{#14163}

webrtc/modules/video_coding/OWNERS

@@ -5,7 +5,7 @@ sprang@webrtc.org
 
 # These are for the common case of adding or renaming files. If you're doing
 # structural changes, please get a review from a reviewer in this file.
+per-file *.gn=*
+per-file *.gni=*
 per-file *.gyp=*
 per-file *.gypi=*
-
-per-file BUILD.gn=kjellander@webrtc.org