Track switch to libinput in xorg-server 1.20.8

Remove the Driver line from examples 5.7 and 5.9, thus making them
valid for both variant configurations of X (with or without libinput).

For 12.1 and xorg-server 1.20.8, add "Set kern.evdev.rcpt_mask=6 in
/etc/sysctl.conf if not using moused" important paragraph to section
"5.4.7.2. Mice and Pointing Devices".

PR: 244820
Submitted by: pauamma
Reviewed by: zeising@
Approved by: bcr@
Differential Revision: https://reviews.freebsd.org/D25641