Move _filter_keys inside _get_formatted_section_data
Move _filter_keys inside _get_formatted_section_data

The filtering of unrecognised keys needs to happen before the section
fields are parsed because they need to be looked up.

alphagov/digitalmarketplace-supplier-frontend,alphagov/digitalmarketplace-supplier-frontend,alphagov/digitalmarketplace-supplier-frontend,alphagov/digitalmarketplace-supplier-frontend