fix: respect LETTERFEED_BACKEND_URL at build time #1

frontend/jest.setup.js

@@ -1,18 +1 @@
-import '@testing-library/jest-dom';
-import fetchMock from 'jest-fetch-mock';
-
-fetchMock.enableMocks();
-
-Object.defineProperty(window, 'matchMedia', {
-  writable: true,
-  value: jest.fn().mockImplementation(query => ({
-    matches: false,
-    media: query,
-    onchange: null,
-    addListener: jest.fn(), // deprecated
-    removeListener: jest.fn(), // deprecated
-    addEventListener: jest.fn(),
-    removeEventListener: jest.fn(),
-    dispatchEvent: jest.fn(),
-  })),
-});
+import '@testing-library/jest-dom'