refactor: messaging naming fixes (#5383)

Some naming fixes we discussed in our team chat and which Lasse
[disliked](AztecProtocol/aztec-packages#5206 (comment))
in my purge PR a few days ago.
\+ nuked some stale stuff from contracts.

aztec/src/messaging.nr

@@ -23,15 +23,15 @@ pub fn process_l1_to_l2_message(
         content,
         secret
     );
-    let entry_key = msg.hash();
+    let message_hash = msg.hash();
 
-    let returned_message = get_l1_to_l2_membership_witness(entry_key);
+    let returned_message = get_l1_to_l2_membership_witness(message_hash);
     let leaf_index = returned_message[0];
     let sibling_path = arr_copy_slice(returned_message, [0; L1_TO_L2_MSG_TREE_HEIGHT], 1);
 
     // Check that the message is in the tree
     // This is implicitly checking that the values of the message are correct
-    let root = compute_merkle_root(entry_key, leaf_index, sibling_path);
+    let root = compute_merkle_root(message_hash, leaf_index, sibling_path);
     assert(root == l1_to_l2_root, "Message not in state");
 
     msg.compute_nullifier()

aztec/src/oracle/get_l1_to_l2_membership_witness.nr

@@ -1,9 +1,9 @@
 use dep::protocol_types::constants::L1_TO_L2_MESSAGE_ORACLE_CALL_LENGTH;
 
-// Checks if a msg is within the l1ToL2Msg tree
+// Obtains membership witness (index and sibling path) for a message in the L1 to L2 message tree.
 #[oracle(getL1ToL2MembershipWitness)]
-fn get_l1_to_l2_membership_witness_oracle(_entry_key: Field) -> [Field; L1_TO_L2_MESSAGE_ORACLE_CALL_LENGTH] {}
+fn get_l1_to_l2_membership_witness_oracle(_message_hash: Field) -> [Field; L1_TO_L2_MESSAGE_ORACLE_CALL_LENGTH] {}
 
-unconstrained pub fn get_l1_to_l2_membership_witness(entry_key: Field) -> [Field; L1_TO_L2_MESSAGE_ORACLE_CALL_LENGTH] {
-    get_l1_to_l2_membership_witness_oracle(entry_key)
+unconstrained pub fn get_l1_to_l2_membership_witness(message_hash: Field) -> [Field; L1_TO_L2_MESSAGE_ORACLE_CALL_LENGTH] {
+    get_l1_to_l2_membership_witness_oracle(message_hash)
 }