Remove SystemD method to mount directory in qemu tutorial
Remove SystemD method to mount directory in qemu tutorial because two methods were mentioned and the fstab method is sufficient. SystemD method adds complexity to tutorial and removes clarity.
From man of systemd.mount:
fstab
Mount units may either be configured via unit files, or via /etc/fstab
(see fstab(5) for details). Mounts listed in /etc/fstab will be converted
into native units dynamically at boot and when the configuration of the system
manager is reloaded. In general, configuring mount points through /etc/fstab is
the preferred approach to manage mounts for humans. For tooling, writing mount
units should be preferred over editing /etc/fstab. See systemd-fstab-generator(8)
for details about the conversion from /etc/fstab to mount units.