Removing TestHelper from FeedService tests.

This removes the overhead imprint.

Tests run at quick speed:

$ rake test:file[test/services/feed_service_test.rb]
test/services/feed_service_test.rb
Rack::File headers parameter replaces cache_control after Rack 1.5.
Run options: --seed 41627

.....

Finished tests in 0.015902s, 314.4225 tests/s, 377.3070 assertions/s.