Previously, notify on deleting a reviewer defaulted to ALL. This
continues to be the case for non-WIP changes.
For WIP changes, we don't want to notify anyone unless this action
results in one or more approvals being removed from the change. If any
approvals are removed, the deleted reviewer and maybe the owner are the
only recipients (which may seem strange but that's existing behavior
when notify=OWNER for this particular notification). If no approvals are
removed, then no notification is sent.
Change-Id: I00821cddb2558fd35c17ae76c47567b8189be0db
8760741834