[chore][exporter/datadog] try fix linter (open-telemetry#39165)

#### Description
Un-deprecate an internal config field. End users will still get warnings
if they set this config.

This seems to introduce flakiness in linters (sometimes linter picks up
the `//nolint:staticcheck` comment, sometimes doesn't). It is not very
clear to me how linters can be flaky but this PR should make it stable

Author: songy23

exporter/datadogexporter/factory.go

@@ -319,7 +319,7 @@ func (f *factory) createMetricsExporter(
 		// Start the hostmetadata pusher once.
 		// It sends the hostmetadata for the host where the collector is running.
 		if cfg.HostMetadata.Enabled {
-			if cfg.HostMetadata.HostnameSource == datadogconfig.HostnameSourceFirstResource { //nolint:staticcheck
+			if cfg.HostMetadata.HostnameSource == datadogconfig.HostnameSourceFirstResource {
 				set.Logger.Warn("first_resource has no effect when serializer exporter is used for exporting metrics")
 			}
 			f.onceMetadata.Do(func() {

exporter/datadogexporter/hostmetadata.go

@@ -15,7 +15,7 @@ func newMetadataConfigfromConfig(cfg *datadogconfig.Config) hostmetadata.PusherC
 		ConfigTags:          cfg.HostMetadata.Tags,
 		MetricsEndpoint:     cfg.Metrics.Endpoint,
 		APIKey:              string(cfg.API.Key),
-		UseResourceMetadata: cfg.HostMetadata.HostnameSource == datadogconfig.HostnameSourceFirstResource, //nolint:staticcheck
+		UseResourceMetadata: cfg.HostMetadata.HostnameSource == datadogconfig.HostnameSourceFirstResource,
 		InsecureSkipVerify:  cfg.TLSSetting.InsecureSkipVerify,
 		ClientConfig:        cfg.ClientConfig,
 		RetrySettings:       cfg.BackOffConfig,

pkg/datadog/config/host.go

@@ -13,8 +13,6 @@ import (
 type HostnameSource string
 
 const (
-	// Deprecated: [v0.124.0] opt in to https://docs.datadoghq.com/opentelemetry/mapping/host_metadata/ instead
-	//
 	// HostnameSourceFirstResource picks the host metadata hostname from the resource
 	// attributes on the first OTLP payload that gets to the exporter. If it is lacking any
 	// hostname-like attributes, it will fallback to 'config_or_system' behavior (see below).