Chapter name was a collection of all heading 1 (and contained heading 2,
heading 3, ...) texts, but just heading 1 itself is enough.

Change-Id: I893a935c4f4855ef5d19a01e2679ba7101af853f
Reviewed-on: https://gerrit.libreoffice.org/41246Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>