[DCLG Newlove] Add missing TNA Timestamp

This site has been crawled so can have a non-fake timestamp.
Merge pull request #904 from alphagov/newlove_new_timestamp

[DCLG Newlove] Add missing TNA Timestamp
Merge pull request #903 from rjc123/directgov

Migrate directgov to transition
Add comment clarifying special_redirect_strategy for this site
Remove directgov tests
Remove Directgov mappings
Remove national archives tests