Revert enhanced bookmarks sync datatype
We'd like to move to a new sync datatype like this, but there's
not an effective way to do it while supporting existing
encrypted bookmarks users. We'll eventually get there by
extending BookmarkSpecifics to do what we need, then
reintroducing the new type and converting client-side once
feasible for all clients.
By the time we're ready to reintroduce the new type many things
will likely have changed, so just remove it for the time being.
This reverts commit
72520cfbda25e457da26113b568c76171d716a3f.
BUG=427727
Review URL: https://codereview.chromium.org/
673983003
Cr-Commit-Position: refs/heads/master@{#301703}