Remove the empty property of attestation.

In GSI images attestation specific properties
(ro.product.*_for_attestation) are empty, which causes attestation
failure on devices with different values in ro.product.* and
ro.product.vendor.* from actual values provisioned in Keymint.

Hence these values added only if they are set in build files.

Bug:294190893
Test: atest CtsKeystoreTestCases:android.keystore.cts.DeviceOwnerKeyManagementTest#testAllVariationsOfDeviceIdAttestation

Signed-off-by: wufei3 <wufei3@xiaomi.corp-partner.google.com>
(cherry picked from https://android-review.googlesource.com/q/commit:99fafaec2245faebb787a0d1f7451557ab4a8fb4)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:51ad31547889c702ae956fe5902a640743d605ca)
Merged-In: Icaf1bcd089767b2c47d0b57064aa72a4c9483bb5
Change-Id: Icaf1bcd089767b2c47d0b57064aa72a4c9483bb5