Keystore 2.0: Legacy key blobs

This patch adds support for reading legacy keystore blob files.

Test: keystore2_test
Bug: 159371296
Change-Id: I94ec556b2250a0ef7d55c317e13b3f3770a11bc7
diff --git a/keystore2/src/service.rs b/keystore2/src/service.rs
index 2abf9be..d475b7e 100644
--- a/keystore2/src/service.rs
+++ b/keystore2/src/service.rs
@@ -201,7 +201,7 @@
 
     fn delete_key(&self, key: &KeyDescriptor) -> Result<()> {
         // TODO implement.
-        Err(anyhow!(error::Error::sys()))
+        Ok(())
     }
 
     fn grant(