Remove CUE replace statement once openapi changes are merged

[sdboyer]

I had to fork CUE for some fixes - there were a couple key cases that weren't covered (conjuncts in numeric value types, selectors on object types). This substantially impacted Go codegen elsewhere, being the difference between obviously incorrect and probably correct.

Originally posted by @sdboyer in #90 (comment)

[sdboyer]

cc @IfSentient you'll need to hoist the replace cuelang.org/go statement from thema's go.mod when you update