[Sync:USS] LoginDatabase::RemoveLogins*() should return a ChangeList

This is a mechanical change that only moves code around to have a more
consistent LoginDatabase API.

For consistency with AddLogin and UpdateLogin, RemoveLogin* methods
should return a PasswordStoreChangeList. This is in preparation for
a later patch that would add the primary key to the
PasswordStoreChangeList.

In addition, this changes makes GetLoginsSyncedBetween() private
and replaces push_back with emplace_back to save moving the relatively
large struct PasswordStoreChangeList as much as possible.

Bug: 902349
Change-Id: Ided5923fbd95768ae3f91179d1dc3648725cbe0b
Reviewed-on: https://chromium-review.googlesource.com/c/1409550
Commit-Queue: Mohamed Amir Yosef <mamir@chromium.org>
Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#623690}
6 files changed