autofill service search uri is not backed up

This is expected as the settings is set by the app market of the device
each time the marked it set up.

Bug: 37684646
Test:  mmma -j40 frameworks/base/core/tests/coretests &&
       adb install -r ${ANDROID_PRODUCT_OUT}/data/app/FrameworksCoreTests/FrameworksCoreTests.apk &&
       adb shell am instrument -w -e class android.provider.SettingsBackupTest com.android.frameworks.coretests/android.support.test.runner.AndroidJUnitRunner

Change-Id: Ie9502150d0861173ab58ed7d096d3900704b8915