Systemd and compat typos

This branch performs two minor fixes.

The first removes the unnecessary zfs-initramfs.triggers file containing an update-initramfs trigger. dh_compat 12 is smart enough to figure out that trigger automatically. This resolves a lintian error.

The second patch removes a typo (zfs-impot rather than zfs-import). However, even if that typo were corrected, the call would not do the right thing: it would process the zfs-import-* units properly, but then process all units (including zfs-import-cache a second time) with the restart. The correct fix would use -X to exclude those files.

Instead, we do not restart any units besides zfs-zed, since those restarts are essentially no-ops (also, and perhaps more importantly, restarting would be very undesirable). This aligns the sysvinit and systemd behavior.