Verify batch proofs once kernel exists

We currently verify a submitted user batch by re-proving it and verifying it matches the submitted proof. This is because the batch proof kernel does not actually do any proving yet - it simply re-verifies the batch's transaction proofs.

Once the batch kernel lands for real, we should switch to verifying it instead.

https://github.com/0xMiden/node/blob/9437942e7b45449779a6d0bc080cf9bf885a5f28/crates/rpc/src/server/api.rs#L475-L483