Remove stale TODOs for crbug.com/515108

Initially, the bug tracked properly separating sync-specific code
from the password_manager core. Later, this decision was reversed
(details on the bug), and the sync layer was dissolved.

The one forgotten TODO comment is obsolete by now, so this CL
removes it.

Bug: 515108

Change-Id: Iad3d97b4e63a32512075d70452a756333c871eec
Reviewed-on: https://chromium-review.googlesource.com/c/1292056
Commit-Queue: Vaclav Brozek <vabr@chromium.org>
Reviewed-by: Vadym Doroshenko <dvadym@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601578}

components/password_manager/core/browser/password_manager_client.h

@@ -179,7 +179,6 @@ class PasswordManagerClient {
 
   // Reports whether and how passwords are synced in the embedder. The default
   // implementation always returns NOT_SYNCING.
-  // TODO(crbug.com/515108): Factor this out of the client to the sync layer.
   virtual SyncState GetPasswordSyncState() const;
 
   // Returns true if last navigation page had HTTP error i.e 5XX or 4XX