Greatly reduce repeated code

functions/api/gme/remove.ts

@@ -1,13 +1,9 @@
+import { jsonError } from "../../common.js";
+
 export async function onRequestPost(context: RequestContext) {
   const { user } = context.data.body;
 
-  if (!user)
-    return new Response('{"error":"No user provided"}', {
-      headers: {
-        "content-type": "application/json",
-      },
-      status: 400,
-    });
+  if (!user) return jsonError("No user provided", 400);
 
   await context.env.DATA.delete(`gamemod_${user}`);