Runner divergence from upstream

When I was poking at privileged mode on the runner, I noticed a few differences from the upstream runner chart.

For example:

1. Where we define the KUBERNETES_PRIVILEGED environment variable: https://gitlab.com/charts/gitlab/blob/master/charts/gitlab/charts/gitlab-runner/templates/_env_vars.tpl#L6 versus https://gitlab.com/charts/charts.gitlab.io/blob/master/charts/gitlab-runner/templates/deployment.yaml#L48
2. We don't seem to be mounting the docker socket anymore, which is probably a good thing but definitely a change: https://gitlab.com/charts/gitlab/blob/master/charts/gitlab/charts/gitlab-runner/templates/deployment.yaml versus https://gitlab.com/charts/charts.gitlab.io/blob/master/charts/gitlab-runner/templates/deployment.yaml#L108

There may be others, but we need to be mindful that we commit these back upstream since we want switch to that as a dependency ultimately, not a sub chart.

We will need to continue to offer a standalone Runner chart, so we shouldn't maintain it twice.