Automatically set packer=none when label-type != curved

[jonathancrabtree]

The default packer is running when label-type=spoke, which means that the font size may vary depending on the number of labels and their relative positions. Ideally the packer should take the label-type into account but right now it only works for the default curved label type, meaning that the simplest short-term fix is to disable it for other label types.