GN: Remove webrtc_base target in favor for rtc_base.
GN: Remove webrtc_base target in favor for rtc_base.

The last reference to the old target name was
removed in https://crrev.com/7c9149860a8a0ca24350d2e80dbc280990a0cbb7

R=perkj@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/33079004

git-svn-id: 03ae4fbe531b1eefc9d815f31e49022782c42458@8179 4adac7df-926f-26a2-2b94-8c16560cd09d

sippet/webrtc,sippet/webrtc,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,aleonliao/webrtc-trunk,aleonliao/webrtc-trunk,krieger-od/webrtc,jchavanton/webrtc,jchavanton/webrtc,jchavanton/webrtc,Alkalyne/webrtctrunk,sippet/webrtc,sippet/webrtc,krieger-od/webrtc,krieger-od/webrtc,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,sippet/webrtc,aleonliao/webrtc-trunk,sippet/webrtc,jchavanton/webrtc,aleonliao/webrtc-trunk,jchavanton/webrtc,krieger-od/webrtc,aleonliao/webrtc-trunk,jchavanton/webrtc,jchavanton/webrtc,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,krieger-od/webrtc,krieger-od/webrtc,aleonliao/webrtc-trunk