[PD-834] Only admin pages need to be  blocked...

... I think. 

@almathew  are there any non-admin pages that need to be blocked by a check for site packages?
@tdphillips , on_admin_page is only true on pages where admin is in the path, so wouldn't always evaluate to true. 

In practice, if we're creating packages like we're supposed to, has_package should always evaluate to true, which would make the second condition useless, but when it's missing, we don't want to hide it on non-admin pages (such as purchasing a job), which is why it's there. In other words, i can't be condensed.