docs: remove some pointless spacing

docs: remove some pointless spacing

The different headers and header-sizes already convey the hierarchical
structure of this document, the unusual spacing arguably just looks a
bit inconsistent with the rest of the site. Let's remove it; it looks
fine without it, and will translate better to other markup languages.

Signed-off-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>