[AF Sync] Remove cache in the wallet metadata sync bridge

This CL removes cache from the wallet metadata bridge. The cache is not
needed in the new design. This CL temporarily regresses on the
functionality to react to local data changes. Thus, it temporarily
disables a couple unit-tests.

Bug: 853688
Change-Id: I86269225589b016fe4fa2ee23d5c1ff99783b0e0
Reviewed-on: https://chromium-review.googlesource.com/c/1402813
Commit-Queue: Jan Krcal <jkrcal@chromium.org>
Reviewed-by: Sebastien Seguin-Gagnon <sebsg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621261}
3 files changed