Don't set key for logfile on Heroku

This fixes the issue reported in #5947. Sidekiq will only log to stdout when this key evals to false, so this can't be forced with an empty string. This change eliminates the key altogether when running on Heroku.

closes #6500

Changelog.md

@@ -4,6 +4,7 @@
 
 ## Bug fixes
 * Redirect to sign in page when a background request fails with 401 [#6496](https://github.com/diaspora/diaspora/pull/6496)
+* Correctly skip setting sidekiq logfile on Heroku [#6500](https://github.com/diaspora/diaspora/pull/6500)
 
 ## Features
 

config/sidekiq.yml

 <% require_relative 'config/load_config' %>
 ---
 :verbose: false
-:logfile: "<%= AppConfig.sidekiq_log unless AppConfig.heroku? %>"
+<% unless AppConfig.heroku? %>
+:logfile: "<%= AppConfig.sidekiq_log %>"
+<% end %>
 :concurrency: <%= AppConfig.environment.sidekiq.concurrency.to_i %>
 :queues:
   - socket_webfinger