WebView: remove unused Token Binding system APIs

These APIs never really launched, and the Token Binding protocol is no
longer supported by the chromium team (which means these APIs have been
broken for some time).

This removes most of the TokenBinding API surface, keeping (and
deprecating) just enough to allow us to still compile and run WebView
APKs.

Bug: 119576150
Test: make update-api
Change-Id: Ia5a4258aac5ed21691ea36a428b4aa7195ff21ca