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

[CastleStar14654]

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.