libimage: drop "internal error" message on regular error

This error can happen in many different cases such a a non existing
image or other kind of pull errors. In all cases they do not reflect any
sort of internal inconsistency in the code itself so this is just
misleading to users.

Fixes: #2465

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

Author: Luap99

libimage/copier.go

@@ -488,7 +488,7 @@ func (c *Copier) copyToStorage(ctx context.Context, source, destination types.Im
 	var resolvedReference types.ImageReference
 	_, err := c.copyInternal(ctx, source, destination, &resolvedReference)
 	if err != nil {
-		return nil, fmt.Errorf("internal error: unable to copy from source %s: %w", transports.ImageName(source), err)
+		return nil, fmt.Errorf("unable to copy from source %s: %w", transports.ImageName(source), err)
 	}
 	if resolvedReference == nil {
 		return nil, fmt.Errorf("internal error: After attempting to copy %s, resolvedReference is nil", source)