Remove Unused and Undocumented Functions accurate_Cast and accurate_CastOrNull

Remove the functions accurate_Cast and accurate_CastOrNull (they are different to accurateCast and accurateCastOrNull by underscore in the name and they are not affected by the value of cast_keep_nullable setting). These functions were undocumented, untested, unused, and unneeded. They appeared to be alive due to code generalization. #40682 (Alexey Milovidov).