Update the embassies YML file with URLs

Note that as of right now, none of our smart answers use the website
key.
Update URLs in Registraions data
Remove external tag for credit payments link
Update FCO links in marriage-abroad-v2 calculator
Update old FCO links in marriage abroad
Update FCO links in overseas-passports
Update tests that used old URLs
Merge pull request #301 from alphagov/removing-fco-links

Removing FCO Links (final batch!)