CI: disable download_chart in .stable job

Summary

Comment download_chart from the .stable CI job base, as it is causing failures. This is not needed, as deploy calls helm repo add ... ; helm dep update .

Details

In a7fbae81 we removed a few lines of download_chart, but didn't want to entirely disable it. Turns out, we should actually have. This full disables download_chart function.

Key items in download_chart (helm init --client-only, helm repo add) are performed in the install_tiller(L270) and deploy (L114) functions so for now, we can safely and entirely disable this.