fix: Remove ref to deleted asset

[kimadactyl]

No idea how this slipped through but this test failing. Note the whole collections system needs removing but this gets CI passing again.

 Error:
CollectionsControllerTest#test_should_show_collection:
ActionView::Template::Error: The asset "2017/12/placecal_winter2017.pdf" is not present in the asset pipeline.

    app/views/collections/show.html.erb:25
    test/controllers/collections_controller_test.rb:12:in `block in <class:CollectionsControllerTest>'

663 tests, 1914 assertions, 0 failures, 1 errors, 0 skips

_{Huly®: PC-2665}

[lenikadali]

Looks good to me.

Note the whole collections system needs removing but this gets CI passing again.

Interesting. Maybe have an issue where this is tracked (so that we don't forget 😅)