GitLab

Removes from ModelTypeController preferences dependent logic
for purging sync metadata.

Now ModelAssociationManager advises data type controllers
when is it necessery to purge sync metadata.

Bug: 823721
Change-Id: Ib4e73fde912accc6b84188d0f21c3df724000f5e
Reviewed-on: https://chromium-review.googlesource.com/1008303
Commit-Queue: Aleksei Loshkarev <lixan@yandex-team.ru>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568775}