Remove rollup-plugin-node-polyfills dependency

[chrispcampbell]

Currently the plugin-check package has a dependency on rollup-plugin-node-polyfills, which is no longer maintained and depends on deprecated packages. There is a replacement (rollup-plugin-polyfill-node) but for our purposes, it would probably be better to just provide our own custom no-op polyfills since the code is not actually used in the browser at runtime. (The polyfills are only needed as fallout from our approach of generating a single "check bundle" that can work in both Node and browser environments.)