Remove /etc/hostid missing warning

No longer print the following warning to the console when the
/etc/hostid file is missing. This is the expected default behavior.
Keeping the hostid in sync with the initramfs is now accomplished
by creating the /etc/hostid in the initramfs not on the system.

SPL: The /etc/hostid file is not found.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>