Remove Channel ID feature from Webview

Bug: 17177684

The feature requires a public api to share channel IDs or disable them.
We will enable the feature after the APIs are added.

The chromium counterpart of this code already landed here:
https://codereview.chromium.org/497963002/

Change-Id: I2ae0b0bf4a9476cf6b2ebc8759c49805f303db6b
2 files changed