promtail: no need for GCP promtail_instance label now that loki supports out-of-order writes

[james-callahan]

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #4474

Special notes for your reviewer:

Checklist

• Documentation updated
• Tests updated

[CLAassistant]

All committers have signed the CLA.

[owen-d]

Great catch. Are you willing to sign the CLA?

[james-callahan]

Great catch. Are you willing to sign the CLA?

Done

[kavirajk]

Thanks @james-callahan. LGTM!.

@owen-d this could be a breaking change. should be add it to the upgrade guide?

[owen-d]

Good call @kavirajk. Let's add a small note to the upgrade guide mentioning the lost label :)

[owen-d]

It also looks like we'll need one small change to pass the linter:

clients/pkg/promtail/targets/gcplog/formatter.go:21:5: var `instanceID` is unused (unused)
186s
19	var instanceID uuid.UUID

[james-callahan]

It also looks like we'll need one small change to pass the linter

Fixed + rebased.

The tests now seem to be failing for unrelated reasons?

[owen-d]

Hey, the reason it's failing is because by removing some code, it's actually changed the expected go.mod configs because the uuid library is now an indirect dependency:

-	github.com/gofrs/uuid v4.0.0+incompatible
+	github.com/gofrs/uuid v4.0.0+incompatible // indirect

You should be able to resolve this by running go mod tidy and committing after.

[james-callahan]

Hey, the reason it's failing is because by removing some code, it's actually changed the expected go.mod configs because the uuid library is now an indirect dependency:

huh. weird that this manifested so far away in the tests (only failures in compactor retention tests); while the lint stage passed.

You should be able to resolve this by running go mod tidy and committing after.

Done.