Revert of [Sync] Erase sync DB when corrupted

Revert of [Sync] Erase sync DB when corrupted (patchset #4 id:60001 of https://codereview.chromium.org/1082893003/)

Reason for revert:
Test fails on Win7 bots. see crbug.com/481895

Original issue's description:
> [Sync] Erase sync DB when corrupted
>
> Directory now registers to be notified of catastrophic sync DB errors.
> Upon notification, Directory triggers an unrecoverable sync error which
> causes ProfileSyncService to delete the sync DB.
>
> Add integration test that verifies the sync DB is deleted when DB
> corruption is detected.
>
> Remove unused member variable allow_failure_for_test_ from
> DirectoryBackingStore.
>
> Add MockUnrecoverableErrorHandler to assist in writing tests for
> Directory.
>
> BUG=470993
>
> Committed: https://crrev.com/90a7f8d3e3b3a2aac43e71a93eac2731f084945c
> Cr-Commit-Position: refs/heads/master@{#327120}

TBR=zea@chromium.org,pvalenzuela@chromium.org,maniscalco@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=470993
Committed: https://crrev.com/6d60180f3ca3f9289d37b27e77f90d97db488f7c
Cr-Commit-Position: refs/heads/master@{#327264}

[vkuzkokov, 2015-04-28 11:26:38]

Created Revert of [Sync] Erase sync DB when corrupted

[commit-bot: I haz the power, 2015-04-28 11:26:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1104423005/1

[commit-bot: I haz the power, 2015-04-28 11:27:44]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-28 11:28:41]

Patchset 1 (id:??) landed as
https://crrev.com/6d60180f3ca3f9289d37b27e77f90d97db488f7c
Cr-Commit-Position: refs/heads/master@{#327264}