Revert "Add createDeferredPromise test util"

This reverts commit b08a63b.

frontend/src/tests/utils/utils.test-utils.ts

@@ -44,31 +44,3 @@ export const isNotVisible = (element: Element): boolean => {
     return nonNullish(heightString) && Number(heightString) === 0;
   }
 };
-
-// Return a promise-like object that exposes its resolve and reject functions.
-export const createDeferredPromise = <T>(): Promise<T> & {
-  promise: Promise<T>;
-  resolve: (value: T) => void;
-  reject: (reason?: unknown) => void;
-} => {
-  let resolve: (value: T) => void;
-  let reject: (reason?: unknown) => void;
-
-  const promise = new Promise<T>((res, rej) => {
-    resolve = res;
-    reject = rej;
-  });
-
-  return {
-    promise,
-    resolve,
-    reject,
-    then: (onFulfilled, onRejected) => promise.then(onFulfilled, onRejected),
-    catch: (onRejected) => promise.catch(onRejected),
-    finally: (onFinally) => promise.finally(onFinally),
-  } as Promise<T> & {
-    promise: Promise<T>;
-    resolve: (value: T) => void;
-    reject: (reason?: unknown) => void;
-  };
-};