Remove/document remaining Electra TODOs (#6982)

Not essential to merge this now, but I'm going through TODOs for Electra to make sure we haven't missed anything.

Targeting this at the release branch anyway so that auditors/readers don't get alarmed 😅

beacon_node/execution_layer/src/lib.rs

@@ -209,6 +209,7 @@ pub enum BlockProposalContents<E: EthSpec, Payload: AbstractExecPayload<E>> {
         /// `None` for blinded `PayloadAndBlobs`.
         blobs_and_proofs: Option<(BlobsList<E>, KzgProofs<E>)>,
         // TODO(electra): this should probably be a separate variant/superstruct
+        // See: https://github.com/sigp/lighthouse/issues/6981
         requests: Option<ExecutionRequests<E>>,
     },
 }