Remove unnecessary type reference in Vitest example (#39819)

Documentation / Examples

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 The examples guidelines are followed from our contributing doc


The Vitest docs state that /// <reference types="vitest" /> is only required when importing defineConfig from vite.

examples/with-vitest/vitest.config.ts

@@ -1,5 +1,3 @@
-/// <reference types="vitest" />
-
 import { defineConfig } from 'vitest/config'
 import react from '@vitejs/plugin-react'