chore(insights): drop the now-unused environment-field label helpers

The correlation-narrative localisation replaced the env-channel narration
labels (which read through getEnvironmentField().narrationLabel) with the
localised insights.correlation.channel.ENV_* keys, leaving these two helpers
dead.

src/lib/environment/fields.ts

@@ -119,13 +119,3 @@ export const ENVIRONMENT_FIELDS: readonly EnvironmentField[] = [
 /** The correlation channel keys, in declaration order. */
 export const ENVIRONMENT_CHANNEL_KEYS: readonly string[] =
   ENVIRONMENT_FIELDS.map((f) => f.key);
-
-/** True for a registered environmental channel key. */
-export function isEnvironmentChannelKey(key: string): boolean {
-  return ENVIRONMENT_CHANNEL_KEYS.includes(key);
-}
-
-/** Resolve a field by its key, or null when unregistered. */
-export function getEnvironmentField(key: string): EnvironmentField | null {
-  return ENVIRONMENT_FIELDS.find((f) => f.key === key) ?? null;
-}