Turbopack: Remove undocumented `turbopack.conditions` configuration (#83237)
This syntax was undocumented, and as far as I can tell, there are no OSS external users of this API: https://sourcegraph.com/search?q=context:global+/turbopack:%28.%7C%5Cn%29*conditions:/&patternType=keyword&sm=0
https://github.com/vercel/next.js/pull/82857 provides a better syntax for defining these conditions that we intend to document.