Secretkeeper TA: Nothing to validate

The Arcs (in context of AuthrGaph Key Exchange) of Secretkeeper never
leave TA & therefore there is no need of validation of shared session.

Test: Builds
Bug: 291228655
Change-Id: I5764d6700ade3c07c99f9e05bcb7b2467c85b956
diff --git a/core/src/ta.rs b/core/src/ta.rs
index c6a6903..de8bc6b 100644
--- a/core/src/ta.rs
+++ b/core/src/ta.rs
@@ -439,7 +439,7 @@
         _shared_keys: &[Vec<u8>],
         _sha256: &dyn Sha256,
     ) -> Result<(), Error> {
-        // TODO: implement
+        // Secretkeeper does not need to validate shared session after successful Key Exchange.
         Ok(())
     }
 }