Remove link to archive.org on projects with Internet Archive archival disabled

[noah-schechter]

Current
Internet Archive archival is optional right now; we also display a button that redirects to archive.org on the source material modals for incidents in projects with Internet Archive archival disabled.

Proposed
We should remove the button from source material modals in projects with IA archival disabled. The link in question either 1) hasn't been archived by anyone yet or 2) has been archived by a third-party. In the first case, the link is useless; in the second, the existence of the button may cause our users to mistakenly believe Atlos is sending their links to IA.