remove redundant copy in ParseToProtobuf

[asmyasnikov]

No description provided.

[asmyasnikov]

temponary for check CI on old versions of go (because minimal version of go in go.mod - 1.14)
before merge - need to remove my changes

[lfittl]

Thanks for the PR! I think that makes sense, but it appears we'd have to raise the go.mod version to allow using the newer syntax (see https://github.com/pganalyze/pg_query_go/actions/runs/17171245591/job/49052448270?pr=139).

Maybe that's reasonable to do? There isn't a particular need I'm aware of to keep supporting older versions than Go 1.20 (and in fact, any version older than 1.23 is already EOL, so anyone using older versions should have upgraded already).

Also it appears older Go versions fail on Windows in CI, so we can't reasonably test older than 1.20 anyway.

[lfittl]

I've made some minor revisions to drop old versions - thanks for the contribution!