hcp: remove duplicated build registration for JSON

In JSON templates, we register the builds to process on HCP at the
initialisation of the Registry.

However, during the HCP breakout, this code was duplicated with a slight
difference for the JSON templates, and the build names were registered
once during initialisation, with the expected full name, and once at the
start of PopulateIteration, with the truncated name.

This caused a bug when processing a template that contains a builder
with both a name and a type, as both would be registered, but only one
would complete, leading to the iteration being unable to complete.

internal/hcp/registry/json.go

@@ -38,11 +38,6 @@ func NewJSONMetadataRegistry(config *packer.Core) (*JSONMetadataRegistry, hcl.Di
 
 // PopulateIteration creates the metadata on HCP for a build
 func (h *JSONMetadataRegistry) PopulateIteration(ctx context.Context) error {
-	for _, b := range h.configuration.Template.Builders {
-		// Get all builds slated within config ignoring any only or exclude flags.
-		h.bucket.RegisterBuildForComponent(b.Name)
-	}
-
 	err := h.bucket.Validate()
 	if err != nil {
 		return err