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

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#8179}
git-svn-id: 917f5d3ca488f358c4d40eaec14422cf392ccec9@8179 4adac7df-926f-26a2-2b94-8c16560cd09d

TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc