Bug fix for current sort value not showing in OS search dropdown

[ltrasca]

Changes in this PR

• Removed mentions of build_sorting_orders in the search endpoints - these weren't needed anymore as we don't pass sorting to the query building functions in that format anymore
• Replaced the sort list template reference on TB search page with a much simpler duplicate, isolated from the sorting on other types of templates. This now uses the sort variable passed to the template context - going forwards a refactor of the original template to use this simpler strategy would be ideal
• Updated tests to reflect changes and removed the build_sorting_orders_open_search deprecated function

JIRA ticket

N/A

Screenshots of UI changes

N/A

• Requires env variable(s) to be updated