chore: remove vitest configuration file as it is no longer needed

frontend/vitest.config.mjs

@@ -1,11 +0,0 @@
-import tsconfigPaths from "vite-tsconfig-paths";
-import { defineConfig } from "vitest/config";
-import react from "@vitejs/plugin-react";
-
-export default defineConfig({
-  plugins: [tsconfigPaths(), react()],
-  test: {
-    environment: "jsdom",
-    setupFiles: ["src/__tests__/setupTests.ts"],
-  },
-});