Removed unused utilities to add/remove source IP in the gRPC metadata

[pracucci]

What this PR does

While working on https://github.com/grafana/mimir/pull/7529, I've noticed that we have utilities to add "source IP" in the gRPC metadata but we never read it (I've also checked GEM). This was introduced almost 4 years ago in Cortex (see PR): at that time we were also reading it in Cortex. I've the feeling this code is actually dead code no more used, so we can remove it (proposed in this PR), but please block me if you're aware such metadata is actually somewhere.

Which issue(s) this PR fixes or relates to

N/A

Checklist

• [ ] Tests updated.
• [ ] Documentation added.
• [ ] CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX].
• [ ] about-versioning.md updated with experimental features.