doc: Fix a duplicate section
doc: Fix a duplicate section

In commit 88aaaab7b, I overlooked that there
was already a doc comment for the flatpak-version-macros
section at the bottom. To make things worse,
the duplicate I added was malformed.
Fix things up to work as intended.

flatpak/flatpak,flatpak/flatpak,flatpak/flatpak,flatpak/flatpak,flatpak/flatpak