`\null` in `\enddeluxetable` adds extra empty line in main text

Line 5102 of `aastex631.cls` add a `\null` after `\end{table}`. This adds an empty box at *main text*, and if empty lines surround the `deluxetable` environment in the source, an empty paragraph will be inserted into main text.

`aastex63.cls` does not have this bug. 