[exporter/datadog] remove exporter.datadog.hostname.preview (#37561)

#### Description
Remove deprecated feature gate `exporter.datadog.hostname.preview`

Author: songy23

.chloggen/ddog-remove-fg.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: breaking
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: datadogexporter
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: "Remove stable feature gate `exporter.datadog.hostname.preview`"
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [37561]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

exporter/datadogexporter/internal/hostmetadata/host.go

@@ -9,7 +9,6 @@ import (
 
 	"github.com/DataDog/opentelemetry-mapping-go/pkg/otlp/attributes/source"
 	"go.opentelemetry.io/collector/component"
-	"go.opentelemetry.io/collector/featuregate"
 
 	"github.com/open-telemetry/opentelemetry-collector-contrib/exporter/datadogexporter/internal/hostmetadata/internal/azure"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/exporter/datadogexporter/internal/hostmetadata/internal/ec2"
@@ -20,14 +19,6 @@ import (
 	"github.com/open-telemetry/opentelemetry-collector-contrib/exporter/datadogexporter/internal/hostmetadata/provider"
 )
 
-var _ = featuregate.GlobalRegistry().MustRegister(
-	"exporter.datadog.hostname.preview",
-	featuregate.StageStable,
-	featuregate.WithRegisterDescription("Use the 'preview' hostname resolution rules, which are consistent with Datadog cloud integration hostname resolution rules, and set 'host_metadata::hostname_source' to 'config_or_system' by default."),
-	featuregate.WithRegisterReferenceURL("https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/10424"),
-	featuregate.WithRegisterToVersion("0.75.0"),
-)
-
 func GetSourceProvider(set component.TelemetrySettings, configHostname string, timeout time.Duration) (source.Provider, error) {
 	ecs, err := ecs.NewProvider(set)
 	if err != nil {