chore: Remove mocking function in EccOpQueue again (#5413)

PR #4854 removed the mocking function from the `EccOpQueue`
`populate_with_mock_initital_data` which was stale and only populating
the `ultra_ops` rather than both `raw_ops` and `ultra_ops` and ensured
mocking (required to avoid commitments to 0) is done everywhere with a
single function
`GoblinMockCircuits::perform_op_queue_interactions_for_mock_first_circuit(op_queue);`.
A mis-merge reintroduced `populate_with_mock_initital_data` so removing
again.

barretenberg/cpp/src/barretenberg/proof_system/op_queue/ecc_op_queue.hpp

@@ -208,30 +208,6 @@ class ECCOpQueue {
         return result;
     }
 
-    /**
-     * @brief TESTING PURPOSES ONLY: Populate ECC op queue with mock data as stand in for "previous circuit" in tests
-     * @details TODO(#723): We currently cannot support Goblin proofs (specifically, transcript aggregation) if there
-     * is not existing data in the ECC op queue (since this leads to zero-commitment issues). This method populates the
-     * op queue with mock data so that the prover of an arbitrary 'first' circuit can behave as if it were not the
-     * prover over the first circuit in the stack. This method should be removed entirely once this is resolved.
-     *
-     * @param op_queue
-     */
-    void populate_with_mock_initital_data()
-    {
-        // Add a single row of data to the op queue and commit to each column as [1] * FF(data)
-        std::array<Point, 4> mock_op_queue_commitments;
-        for (size_t idx = 0; idx < 4; idx++) {
-            auto mock_data = Fr::random_element();
-            this->ultra_ops[idx].emplace_back(mock_data);
-            mock_op_queue_commitments[idx] = Point::one() * mock_data;
-        }
-        // Set some internal data based on the size of the op queue data
-        this->set_size_data();
-        // Add the commitments to the op queue data for use by the next circuit
-        this->set_commitment_data(mock_op_queue_commitments);
-    }
-
     /**
      * @brief Get the number of rows in the 'msm' column section o the ECCVM, associated with a single multiscalar mul
      *