Revert "- Install missing files by switching from using specified list of"

This reverts commit 11c310f42107295f2be4f2b9a099ee10ec984db0.
downgrade sysutils/syslinux to 4.07

downgrade because of regressions in 6.x (and probably 5.x)
- gpxelinux.0 does not boot
- pxelinux.0 does not boot memtest86+ with serial console option