go_binary: don't concatenate headers in c-archive, c-shared link modes

The `go_binary_c_archive_shared` macro declares several additional targets around `go_binary` rules with `linkmode = "c-shared"` or `"c-archive"`. One of these gathers all the .h files in the `cgo_exports` output group and concatenates them into a single header.

This is not what the Go command does. Only the export header for the `main` package should be visible. Incorporating headers from other packages adds confusion.

Start with the go_binary_c_archive_shared macro and its go_binary rules using linkmode = "c-shared" or "c-archive". Inspect how the cgo_exports output group is gathered and compare it with the Go command's export-header behavior; done means only the main package's export header is visible, without concatenated headers from other packages.

Written by the indexing model from the issue text.