Do not restore settings marked as preserved in SettingsBackupAgent

Bug: 144838882
Test: atest SettingsProviderTest:SettingsBackupAgentTest
      Manual: 1) Run backup for settings
              2) Change several settings
	      3) Run restore for settings
	      4) Through adb logcat verify settings changed in 2) are
	      not  restored

Change-Id: Id309a9417b992eddddb9fe2830f2a691224af9af