docs(migration): remove v4 migration file (#4221)
docs(migration): remove v4 migration file (#4221)

This migration file was meant to be temporary to take note of changes during v4 development. It is now available and maintained on the official [Algolia website](https://www.algolia.com/doc/guides/building-search-ui/upgrade-guides/js/#upgrade-from-v3-to-v4).
algolia/instantsearch.js,algolia/instantsearch.js,algolia/instantsearch.js