Adding shampson (me) as an owner to pc/ & api/.

With deadbeef removed from these OWNERS files, Steve is the only OWNER
on our team. I'm adding myself, because I have worked in these
directories and it makes sense to be able to distribute the code
reviews.

NOTRY=True

Bug: None
Change-Id: I48e88a07ee42254d937391f500f273656853d98b
Reviewed-on: https://webrtc-review.googlesource.com/86980
Commit-Queue: Steve Anton <steveanton@webrtc.org>
Reviewed-by: Steve Anton <steveanton@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23826}

api/OWNERS

@@ -7,6 +7,7 @@ tkchin@webrtc.org
 tommi@webrtc.org
 kwiberg@webrtc.org
 steveanton@webrtc.org
+shampson@webrtc.org
 
 per-file peerconnection*=hbos@webrtc.org
 

pc/OWNERS

@@ -3,6 +3,7 @@ hta@webrtc.org
 juberti@webrtc.org
 perkj@webrtc.org
 pthatcher@webrtc.org
+shampson@webrtc.org
 steveanton@webrtc.org
 tommi@webrtc.org
 zhihuang@webrtc.org