Remove host_name parameter from performance-mongo
Remove host_name parameter from performance-mongo

This was added recently in f74b0afe2485be59bfdda03b27e400d6d00963f4
so I didn't catch it when merging ff25898d5006386e2c8ed0956383f2548b0305d0
to master.

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet