Partially revert ag/17450859

Since the server side change cl/437846745 and
cl/438092010 were merged, the test-only attribute can be
added into the test package, rather than using the platform
certificate to bypass Settings provider @Readble check.

Bug: 227000266
Test: atest FrameworksTelephonyTests
Change-Id: I8926175931cf7a764e1564215ccf64170092ab43