Check for dynamic summaries at display time for search

In order to hide dynamic summaries which use SettingPref,
we check if the summary is equal to "%s".

This is a temporary, band-aid fix which should be
changed in the next release.

Bug: 36101902
Test: make RunSettingsRoboTests
Change-Id: I6cadb3ba68f09ba18ad9a6d2a817804c5d4a08e5