chore: slim down webpack config
chore: slim down webpack config

turns out we only ever used the version-env for sentry. as we recently got rid
of sentry, we can now get rid of that version-env.

we also do some syntactic trickery here to reduce noise and remove some default
args to the compression plugin.

dcos/dcos-ui,dcos/dcos-ui,dcos/dcos-ui,dcos/dcos-ui,dcos/dcos-ui