Reword/reorder the bit about enums without backing types to make it obvious that new code shouldn't do this.

PiperOrigin-RevId: 678817890
Change-Id: Ic4c0597a3696e93b517a146ec4e0a2f738a2fdd0
1 file changed
tree: a87a9438994c6a9d02a90b5ad21eb79602d5cf5e
  1. api-guidelines/