Remove redundant config
Remove redundant config

The sassLint option was removed in https://github.com/alphagov/govuk-jenkinslib/pull/80
And the Yarn install step is unnecessary as of https://github.com/alphagov/govuk-jenkinslib/pull/82
alphagov/finder-frontend,alphagov/finder-frontend,alphagov/finder-frontend,alphagov/finder-frontend