Remove temporary Metrics/BlockLength config from Rubocop config
Remove temporary Metrics/BlockLength config from Rubocop config

The mentioned PR and the FIXME comment was merged, so we don't need this custom
config anymore.

alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf