(maint) Remove unused env variables from Rakefile
(maint) Remove unused env variables from Rakefile

Tests fail on Jenkins because genconfig is unexpectedly skipped.
genconfig is skipped depending on HOSTS or CONFIG being set in the environment.
Currently we use neither value for anything, and always use genconfig; so just remove this.

puppetlabs/pxp-agent,puppetlabs/pxp-agent,puppetlabs/pxp-agent