change ChatPromptFiles to not be a previewFeature (microsoft#256568)

* change ChatPromptFiles to not be a previewFeature

* change according to review

Author: aeschli

src/vs/workbench/contrib/chat/browser/chat.contribution.ts

@@ -414,9 +414,7 @@ configurationRegistry.registerConfiguration({
 			policy: {
 				name: 'ChatPromptFiles',
 				minimumVersion: '1.99',
-				description: nls.localize('chat.promptFiles.policy', "Enables reusable prompt and instruction files in Chat sessions."),
-				defaultValue: false,
-				tags: [PolicyTag.Account, PolicyTag.Preview]
+				description: nls.localize('chat.promptFiles.policy', "Enables reusable prompt and instruction files in Chat sessions.")
 			}
 		},
 		[PromptsConfig.INSTRUCTIONS_LOCATION_KEY]: {