This change removes the in-tree documentation in favor of the one hosted on
the Google's Developer site. This makes it easier to maintain for the
sandbox team, as there is now only a single source of truth for both internal
and external documentation.
If you find errors/bugs in the documentation, please file regular GitHub
issues.
PiperOrigin-RevId: 267132623
Change-Id: I4c950fcef77da0b361cb35b99aa2f187efe6f320