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This has all been replaced by mappings in data/mappings/businesslink.csv and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

I think data/mappings/businesslink_piplinks.csv was cruft that wasn't actually used by anything, given 01b45dfae8bd4174c8effb30b63c2943480c907f