Chromad: Fix nonexisting Polymer observer

Remove referring to the non-existing observer "realmChanged_" from the
"realm" property definition in offline-ad-login.

This fixes the following warning printed by Polymer:

  [offline-ad-login::_observerEffect]: observer method `realmChanged_` not defined

Bug: none
Change-Id: I95cf1f56ca5a3fd8012b88d401e7f5ac270408de
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1623088
Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Reviewed-by: Denis Kuznetsov <antrim@chromium.org>
Commit-Queue: Maksim Ivanov <emaxx@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662132}
1 file changed