No.10 page should not require / use Adobe Flash

As discovered by @joelanman, the No.10 history page appears to require Adobe Flash - with it blocked you get the below warning. It also has non standard navigation.

whitehall/app/views/histories/10_downing_street.html.erb

Line 326 in a41ef2e

    
           <%= javascript_include_tag 'tour/tour_pano.js', integrity: true, crossorigin: 'anonymous' %>

As far as I'm aware, we avoid / don't allow flash on GOV.UK. Hoping this can be escalated.

Link to page: https://www.gov.uk/government/history/10-downing-street

Will discuss with the Content Community

Chatted to Abigail Waraker and they have raised this for their team to look at.

A WIP branch with the tour deleted:
https://github.com/alphagov/whitehall/compare/delete-tour

Currently awaiting new copy for page:
https://trello.com/c/mCfPlz3z/1089-remove-flash-player

Undoes #474