Use startActivity for android.settings.APP_SEARCH_SETTINGS

The Activity launched by android.settings.APP_SEARCH_SETTINGS
does not setResult. So it's no meaning to use
startActivityForResult for the Intent.

Bug: 196923591
Test: manual
      Settings -> Search settings -> search an item ->
      click back button twice and back to Settings home.
Change-Id: Ia760a301465bb87814326611a1ec2368887f120a