Don't show prorating text, when not prorated.

[rebeccacremona]

I somehow failed to commit a change intended to ship with https://github.com/harvard-lil/perma/pull/3774/changes: I didn't commit my changes to the template file, so you see

instead of

Whoops!

This PR fixes that oversight.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.89%. Comparing base (60d0f95) to head (05118be).
⚠️ Report is 5 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3777      +/-   ##
===========================================
+ Coverage    69.87%   69.89%   +0.01%     
===========================================
  Files           73       73              
  Lines         8029     8034       +5     
===========================================
+ Hits          5610     5615       +5     
  Misses        2419     2419              

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