Revert "Unify clearing of sync prefs"

This reverts commit 44d3aa82c83566d5d64d2ae4c297b0510f4072b0.

Reason for revert: suspect of running into sync protocol violations and the corresponding DCHECK failures.

Original change's description:
> Unify clearing of sync prefs
> 
> SyncPrefs is a thin layer on top of preferences and hosts two groups
> of preferences:
> 1) Actual user-facing settings, such as type-selection, exposed via
>    SyncUserSettings.
> 2) Local "bookkeeping" sync metadata, such the last synced time or the
>    client ID (cache GUID).
> 
> In addition, there are two cases that fall somewhere in the middle,
> whose behavior is changed in this patch:
> a) FirstSetupComplete: which roughly represents the user having
>    consented to sync-the-feature (as opposed to transport-only upon
>    sign-in without explicit user consent).
> b) The encryption-bootstrap-token: which represent an explicit
>    passphrase (usually custom passphrase) entered by the user, that
>    allows decrypting the incoming sync changes and encrypt outgoing
>    ones.
> 
> The last two preferences above fit group 1 better, so this patch stops
> clearing them in SyncPrefs::ClearPreferences(), now renamed to
> SyncPrefs::ClearLocalSyncTransportData().
> 
> With such cleanup, what used to be
> ClearDirectoryConsistencyPreferences() is now merged into a single
> clearing function, ClearLocalSyncTransportData(), and all calling sites
> are unified by directly clearing prefs in ShutdownImpl(DISABLE_SYNC), as
> opposed to individual calling sites.
> 
> This introduces -arguably desirable- behavioral changes because
> codepaths like RESET_LOCAL_SYNC_DATA or STOP_SYNC_FOR_DISABLED_ACCOUNT
> now actually clear all local metadata, which most notably includes
> keystore keys.
> 
> Change-Id: I2c42f98c4e068c7e340580d0b78a5cd5b5c46171
> Bug: 1046237
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2023649
> Commit-Queue: Mikel Astiz <mastiz@chromium.org>
> Reviewed-by: Marc Treib <treib@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#735841}

TBR=treib@chromium.org,mastiz@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1046237, 1048771
Change-Id: I4ce9e941f12aa58b7b6b286e990e74a1e01dad69
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2043451
Commit-Queue: Rushan Suleymanov <rushans@google.com>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#739374}

• chrome/browser/sync/test/integration/single_client_polling_sync_test.cc[diff]
• components/sync/base/sync_prefs.cc[diff]
• components/sync/base/sync_prefs.h[diff]
• components/sync/base/sync_prefs_unittest.cc[diff]
• components/sync/driver/profile_sync_service.cc[diff]
• components/sync/driver/profile_sync_service_unittest.cc[diff]