hwclock: squash custom errno strings

hwclock: squash custom errno strings

hwclock previously used printf for custom errno messages.
Later they were converted to use warn(), but were not
squashed. One of the reasons for warn and errno is to avoid
making translators deal with a multitude custom strings.

Also the custom strings are incorrect:

hwclock --hctosys
hwclock: Must be superuser to set system clock.
Unable to set system clock.

We do not know what the system permissions are set to.  The
correct response is to simply say permission was denied; as
the default errno string does. The second line is redundant
and just adds noise the code and to logs.

Patched:

hwclock --hctosys
hwclock: settimeofday() failed: Operation not permitted

Signed-off-by: J William Piggott <elseifthen@gmx.com>