it seems the only way is to comment out the C++ code in Engine\Source\Runtime\Engine\Private\DefaultPawn.cpp:111~112
UPlayerInput::AddEngineDefinedAxisMapping(FInputAxisKeyMapping("DefaultPawn_MoveUp", EKeys::E, 1.f));
UPlayerInput::AddEngineDefinedAxisMapping(FInputAxisKeyMapping("DefaultPawn_MoveUp", EKeys::Q, -1.f));