Refinement of default "Nearby devices" grants.

These grants were initially treated as "system fixed" to remain
consistent with the previous ALWAYS_LOCATION_PERMISSIONS grant, but
these new permissions don't need to be "system fixed".

Bug: 181813006
Test: atest CtsPermission2TestCases
Test: atest CtsPermission3TestCases
Test: atest CtsStatsdAtomHostTestCases
Change-Id: Iea530b620e9cc9824d7e13e3d62975c7c63691bc