Don't back up night display state settings

Bug: 38352336
Test: Turn on night display, then run 'adb shell bmgr transport
android/com.android.internal.backup.LocalTransport && adb shell bmgr
backupnow com.android.providers.settings'. Turn night display off, then
run 'adb shell bmgr restore com.android.providers.settings'. Night display
should not turn back on.
Change-Id: I9ca9474cba9b195850af04ce9d89cbbbd200673b