[go] Disable use of company-go when gopls is used

[rawenous]

The default backend for go-layer is lsp but company-go was still added to company-backends forcing it to search for gocode which should not be used since the user wants lsp.

This change only adds company-go to company-backends if go-mode is selected as the backend.

Note: go-mode is deprecated and gocode is not maintained anymore

[rawenous]

This may not be the optimal way of solving this so please let me know if there is a more correct emacs/spacemacs way.

This seems to solve #11217 and adds the last cleanup needed for #13863

[smile13241324]

I think you should rather put a condition on the company go package itself so that it is not installed at all, right now we are installing it but never use it.

A good example for this is the package flycheck-golangci-lint.

[rawenous]

Thanks. I will take a look at it.