[Thesis links] Rejected thesis link requests remain in the unvetted list

Bug Report

Description

When a thesis link request is rejected, the request stays in the unvetted requests list https://scipost.org/theses/unvetted_thesislinks

Behavior

Expected: Rejecting a thesis link request should remove it from https://scipost.org/theses/unvetted_thesislinks

Actual: The link request stays in https://scipost.org/theses/unvetted_thesislinks, prompting vetting again