Device ID attestation for Corp-owned Profile Owner: follow-up

A small clean-up CL to follow-up on two comments from the original
review:
* Remove the new permission from privapp-permissions-platform.xml as it
is a signature-level permission, not a privileged premission, and as
such does not need to be in that file.
* Do not store the grant state if it's set to false - since the
de-serialization code will only care if there's a "true" value stored.

Bug: 111335970
Test: Manual
Test: atest FrameworksServicesTests:DevicePolicyManagerTest
Test: atest com.android.cts.devicepolicy.MixedProfileOwnerTest#testKeyManagement
Test: atest com.android.cts.devicepolicy.MixedManagedProfileOwnerTest#testKeyManagement
Test: atest com.android.cts.devicepolicy.MixedDeviceOwnerTest#testKeyManagement
Test: atest CtsDevicePolicyManagerTestCases:com.android.cts.devicepolicy.MixedManagedProfileOwnerTest#testDeviceIdAttestationForProfileOwner
Test: atest CtsDevicePolicyManagerTestCases:com.android.cts.devicepolicy.MixedManagedProfileOwnerTest#testDelegatedCertInstallerDeviceIdAttestation
Test: atest CtsDevicePolicyManagerTestCases:com.android.cts.devicepolicy.MixedDeviceOwnerTest#testDelegatedCertInstallerDeviceIdAttestation
Change-Id: I8b570220f5652846fccc53b5e4daaa57f89eb824