pkg: clean up builtin errors
- delete dead code and unused fields
- remove unused arguments
- dedup errors
- use OpContext-based error methods (for positions)
Fixes #902
Issue #52
Change-Id: Idf96e569400a6a5230a8783b0881a895026a41ae
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/9449
Reviewed-by: CUE cueckoo <cueckoo@gmail.com>
Reviewed-by: Paul Jolly <paul@myitcv.org.uk>