On-device signing: Use correct deleteKey() instance.

Use the one that isn't for blobs.

Bug: 190711210
Test: TEST_MAPPING
Change-Id: Ia77cbb8a94cfe96d4dc511e60b9e0b5da384eae6
diff --git a/ondevice-signing/KeystoreHmacKey.cpp b/ondevice-signing/KeystoreHmacKey.cpp
index d917501..09677d7 100644
--- a/ondevice-signing/KeystoreHmacKey.cpp
+++ b/ondevice-signing/KeystoreHmacKey.cpp
@@ -260,7 +260,7 @@
 }
 
 Result<void> KeystoreHmacKey::deleteKey() const {
-    auto status = mSecurityLevel->deleteKey(mDescriptor);
+    auto status = mService->deleteKey(mDescriptor);
     if (!status.isOk()) {
         return Error() << "Failed to delete HMAC key: " << status;
     }