Deployment guide: Adjust headers, spacing

Removing unnecessary hierarchy, fixing glitchy hierarchy, optimizing for TOCs,
standardizing spacing.
Deploy guide: Clarify roles, update language for PE3 all-in-one/one-for-all split

I think we updated this page before the PE team changed the installer to
disallow free-form mixing of roles, and at least one user ran into trouble
trying to put the console and DB on the same node.