* [C++] Fix compiler error from deleted assignment operator (#6036)
The assignment operator of the `buf_` member is deleted, we cannot call it from the assignment operator of the `TableKeyComparator` struct.
=> Also delete the assignment operator of the `TableKeyComparator` struct (already private anyhow).
* [C++] Fix compiler error from deleted assignment operator (#6036) - fix extraneous semicolon
The assignment operator of the `buf_` member is deleted, we cannot call it from the assignment operator of the `TableKeyComparator` struct.
=> Also delete the assignment operator of the `TableKeyComparator` struct (already private anyhow).
