cmd/cue: remove duplicate files from get_go_types.txt
This test includes a few expected output "golden" files for generated
CUE from "cue get go". So, for instance, pkg1/alias_go_gen.cue gets
generated and compared with the expected pkg1/alias_go_gen.cue.golden.
However, the regular output files are included too, for some reason.
It doesn't seem to serve any purpose, as the files are overwritten, and
they are practically duplicates; they just haven't been kept in sync,
as updating golden files via CUE_UPDATE left the other files to bit rot.
Change-Id: Ie92aac38b99471affba139222893b1de99191630
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/536196
Reviewed-by: Roger Peppe <rogpeppe@gmail.com>