Simplify rollup config file

[swiing]

rollup.config.mjs in packages/react declares import statements which values are never read:

import replace from '@rollup/plugin-replace'
import terser from '@rollup/plugin-terser'
import {visualizer} from 'rollup-plugin-visualizer'
import postcss from 'rollup-plugin-postcss'

Consider deleting those lines.

Also, please consider removing the related dependencies, if appropriate, as per #6970 .