Remove memberlist config from ring config.

[kavirajk]

What this PR does / why we need it:
Remove memberlist_config from ingestor_config and distributor_config. Its invalid to provide memerlist_config on these configs.

Which issue(s) this PR fixes:
Fixes #2754

Special notes for your reviewer:

Checklist

• Documentation added
• Tests updated

[owen-d]

(This is a top level config, this is fixing a docs mistake)

[danpoltawski]

Disappointed my pull request tackling the same problem a week ago couldn't be reviewed, was excited to contribute to the project #3505

[owen-d]

Apologies and totally not our intention; we cleaned this up during the bug scrub today. We were looking at issue #2754 but it looks like there were a few issues related to this.

Anyways, we definitely appreciate and want to encourage external contributions and I'm sorry we failed you there. It's difficult for us to keep up will everything.

[danpoltawski]

No worries, there is also #3498 which this partially fixes

[owen-d]

Thanks for the heads up :). The Loki team is very small and some of us are being pulled in a few different directions these days. I rarely get to keep up with the PRs/issues like I used to. I expect that will improve again soon (at least in my case), but I can promise we're trying.

[owen-d]

By the way, it looks like we missed this bit from your PR: https://github.com/grafana/loki/pull/3505/files#diff-025adfc5a8f641b9f5a1869996e3297b6c17f13933f52354cd9b375548ad7970R169-R171

Would you mind opening another with this change? I'll merge it for you!

[kavirajk]

@danpoltawski apologies!. Also didn't notice that your PR is linked to this issue!. You are welcome to add the missing bit like @owen-d suggested :)