docs: remove unneded key in completion plugin

Author: ivictbor

adminforth/documentation/docs/tutorial/05-Plugins/06-text-complete.md

@@ -37,8 +37,6 @@ export const admin = new AdminForth({
     ...
 //diff-add
     new TextCompletePlugin({
-//diff-add
-      openAiApiKey: process.env.OPENAI_API_KEY as string,
 //diff-add
       fieldName: 'title',
 //diff-add