feat(sumologicexporter): remove setting source headers

[aboguszewski-sumo]

Resolves #255
Ref: #685

This PR removes the functionality of setting source headers in the sumologic exporter, which has been deprecated some time ago.

[sumo-drosiek]

Do we need it?

[aboguszewski-sumo]

I'm not sure if we really need it. I found some time ago that such warnings have been printed so I added it.
It was also added for attribute translation and telegraf metrics translation.

[sumo-drosiek]

We added that because it was deprecated, now it's going to be removed :)

[aboguszewski-sumo]

The first such warning was this:

sumologic-otel-collector/pkg/exporter/sumologicexporter/config.go

Lines 128 to 134 in 19c766e

	if len(cfg.MetadataAttributes) > 0 {
	return fmt.Errorf(`*Deprecation warning*: metadata_attributes is not supported anymore.
	Please consult the changelog at https://github.com/SumoLogic/sumologic-otel-collector/releases/tag/v0.49.0-sumo-0`,
	)
	}

[swiatekm]

I think this is ok, but it probably shouldn't say deprecation warning.

[aboguszewski-sumo]

@sumo-drosiek @swiatekm-sumo what's the conclusion then? I'm not against any of the options, but if we don't want it here, we should probably also remove these warnings for other deleted options.

[swiatekm]

I'd leave the error message, just without calling it a deprecation. WDYT @sumo-drosiek ?

[sumo-drosiek]

@swiatekm-sumo we can do that