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

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

layers/+lang/go/packages.el

@@ -46,7 +46,8 @@
 (defun go/init-company-go ()
   (use-package company-go
     :defer t
-    :init (spacemacs|add-company-backends
+    :init (when (eq go-backend 'go-mode)
+            spacemacs|add-company-backends
             :backends company-go
             :modes go-mode
             :variables company-go-show-annotation t)))