Simplify CodecManager::RegisterEncoder()
Simplify CodecManager::RegisterEncoder()

BUG=webrtc:5028

Review URL: https://codereview.webrtc.org/1483963002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#10855}

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