Remove leftover special piplinks code

This has all been replaced by mappings in data/mappings/businesslink.csv and
data/mappings/businesslink_ukwelcomes.csv. This was done in:
e88b588cc3383ca1356ff353f56d94af1b28ab02
and:
39299ffa921c18e14fe0fdd2c734053bf24c59b6
Merge pull request #845 from alphagov/remove_leftover_special_piplinks_code

Remove leftover special piplinks code