61556230 fix change feed issues

This change is for https://www.pivotaltracker.com/story/show/61556230

Passes actual date to change feed endpoint so that we could filter change feed too. Reason is quite complicated: we used to only fetch the relevant Commodity/Heading/Chapter when fetching changes. If we fetch Chapter that was valid on 2000-01-01 and then try to fetch changes with actual date of today (because it wasn't passed)  this will fail because chapter's associations are using this date and Chapter of 2000 won't have valid associations in 2013. This results in some undefined method errors.

Also removes some unused code

Requires merge on backend: https://github.com/alphagov/trade-tariff-backend/pull/130