The `mutated` parameter is never used at any call site - all callers pass `nullptr`.
The explicit comment in `validation.cpp` explains the reason:
// The malleation check is ignored; as the transaction tree itself
// already does not permit it, it is impossible to trigger in the
// witness tree.
These remaining miscellaneous changes were identified by commenting out
the `operator const uint256&` conversion and the `Compare(const uint256&)`
method from `transaction_identifier.h`.
