Revert "feat(rest/request_manager): support for multiple attachments (#484)" (#498)

This reverts commit 34ce39697a.

src/rest/request_manager.ts

@@ -1,10 +1,5 @@
 import { authorization, eventHandlers } from "../bot.ts";
-import {
-  Errors,
-  FileContent,
-  HttpResponseCode,
-  RequestMethods,
-} from "../types/mod.ts";
+import { Errors, HttpResponseCode, RequestMethods } from "../types/mod.ts";
 import {
   API_VERSION,
   BASE_URL,
@@ -160,16 +155,8 @@ function createRequestBody(body: any, method: RequestMethods) {
   }
 
   if (body?.file) {
-    if (!Array.isArray(body.file)) body.file = [body.file];
-
     const form = new FormData();
-    // form.append("file", body.file.blob, body.file.name);
-
-    body.file.map((file: FileContent, index: number) =>
-      // The key of the form data item must be unique; otherwise, Discordeno only considers the first item in the form data with the same names.
-      form.append(`file${index + 1}`, file.blob, file.name)
-    );
-
+    form.append("file", body.file.blob, body.file.name);
     form.append("payload_json", JSON.stringify({ ...body, file: undefined }));
     body.file = form;
   } else if (