Amend tests on GSI that rely on RKP-only props

GSI replaces the values for remote_prov_prop properties (since they’re
system_internal_prop properties), so on GSI the properties are not
reliable indicators of whether StrongBox/TEE are RKP-only or not.

Also included is the removal of the helper skipAttestKeyTestIfNeeded()
so the skipping can happen in the tests directly.

Bug: 348159232
Test: VtsAidlKeyMintTargetTest
Change-Id: I2075e1f76ddd0f87620a212e1aa389803139a117
diff --git a/security/keymint/aidl/vts/functional/KeyMintAidlTestBase.h b/security/keymint/aidl/vts/functional/KeyMintAidlTestBase.h
index 1bf2d9d..0368bba 100644
--- a/security/keymint/aidl/vts/functional/KeyMintAidlTestBase.h
+++ b/security/keymint/aidl/vts/functional/KeyMintAidlTestBase.h
@@ -104,7 +104,7 @@
     uint32_t boot_patch_level();
     bool isDeviceIdAttestationRequired();
     bool isSecondImeiIdAttestationRequired();
-    bool isRkpOnly();
+    std::optional<bool> isRkpOnly();
 
     bool Curve25519Supported();
 
@@ -356,7 +356,6 @@
     bool is_strongbox_enabled(void) const;
     bool is_chipset_allowed_km4_strongbox(void) const;
     bool shouldSkipAttestKeyTest(void) const;
-    void skipAttestKeyTestIfNeeded() const;
 
     void assert_mgf_digests_present_or_not_in_key_characteristics(
             const vector<KeyCharacteristics>& key_characteristics,