[cts content tests] use v4 flag instead of prebuilt APKs Cleaning up prebuilt APKs/idsig files. Will move v2/v3 tests to cts/appsecurity. Will merge PackageManagerShellCommand*Test in a follow-up CL. BUG: 149354175 Test: atest PackageManagerShellCommandIncrementalTest Test: atest PackageManagerShellCommandTest Change-Id: I0363c9c1d89a6ee540d0bc6fe6e4918ad4fcde5e