Revert 97482 - Apps/Extensions Sync refactoring -- delete most of the old glue, implement new syn...

Revert 97482 - Apps/Extensions Sync refactoring -- delete most of the old glue, implement new sync API.

This should maintain current behavior; there are still a number of edge cases around sync + network issues/changing extension versions/etc. that are not fixed by this change.

Reviewers:

akalin: everything
asargent: sanity check around ExtensionService/Extension/ExtensionSyncData

BUG=83983
TEST=sync tests pass, browser tests pass, manually adding/removing extensions/apps works.

Review URL: http://codereview.chromium.org/7564037

TBR=bolms@chromium.org
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=97483