patches: Drop obsolete patches

The patches

  backport/apparmor-allow-default-pki-path.patch
  backport/apparmor-allow-libvirtd-to-call-pygrub.patch
  backport/apparmor-allow-libvirtd-to-call-virtiofsd.patch
  backport/tools-fix-libvirt-guests.sh-text-assignments.patch
  backport/virdevmapper-Don-t-cache-device-mapper-major.patch
  backport/virdevmapper-Handle-kernel-without-device-mapper-support.patch
  backport/virdevmapper-Ignore-all-errors-when-opening-dev-mapper-co.patch

are now included upstream, while

  debian/Prefer-sbin-over-usr-sbin.patch

is no longer necessary because Meson already follows the search
order we want.