JOSS paper reference: Duplicated URLs

[WeiqunZhang]

In the JOSS submission (openjournals/joss-reviews#9530), the URL for de Frahan, Young, Sitaraman, Rood, & Larsen (2023) appears twice. Maybe the url in howpublished can be removed.

[nileshsawant]

Removed the howpublished field [ https://github.com/NatLabRockies/marbles/commit/6e90f178b3e2482f5732b116d9d9d20332e69ff1 ] . Thanks @WeiqunZhang .