view: delete an incorrect comment about a race

Unlike in `Transaction::commit()`, in the `view` module, we actually
don't update the `.jj/view/op_heads/` directory until after we've
recorded the index associated with the operation, so there's no race
there.

lib/src/view.rs

@@ -365,7 +365,6 @@ fn merge_op_heads(
         metadata: operation_metadata,
     };
     let merge_operation_id = op_store.write_operation(&merge_operation).unwrap();
-    // TODO: Like in Transaction::commit(), there's a race here.
     index_store
         .associate_file_with_operation(merged_index.as_ref(), &merge_operation_id)
         .unwrap();