Sidenav logic creating empty sublist

[mejiaj]

Logic in sidenav is creating an empty unordered subnav list. We should correct this to have clean markup.

https://github.com/GSA/plainlanguage.gov/blob/e5f1546b2a4d186c37c4b8790ae368c97e41f2c4/_includes/sidenav.html#L14-L22

Results url: https://www.plainlanguage.gov/law/page-template/

[nick-mon1]

This will be closed out when site is migrated.