Change to using sysprop for services.core.unboosted

The configstore service was deprecated. So change to use sysprop
instead of configstore

Bug: 124531214
Test: 1. check reading property values
      2. uninstall configstore && check reading property values
      3. uninstall configstore && check reading default values
Change-Id: Ia4471a58fdc042d3a011d965582c2ec02f338f3c