cue: cleanup before implementing close structs
cue: cleanup before implementing close structs

Change-Id: I20580bf73a920a015ecc792c90f479e8efb10148
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/2703
Reviewed-by: Marcel van Lohuizen <a22d082192f3ccf984644a4f482781f4c2d65180@golang.org>

cuelang/cue