libxml2: update to 2.10.2 (closes #19288)

This fixes:
- CVE-2022-2309

Release Notes:
- https://gitlab.gnome.org/GNOME/libxml2/-/releases/v2.10.0
- https://gitlab.gnome.org/GNOME/libxml2/-/releases/v2.10.1
- https://gitlab.gnome.org/GNOME/libxml2/-/releases/v2.10.2

Also drop removed docbook compile switch.
Disable PKG_FIXUP to allow backporting.

Signed-off-by: Nick Hainke <vincent@systemli.org>
Signed-off-by: Michael Heimpold <mhei@heimpold.de>