cmds/dmesg: use unix.Klogctl
cmds/dmesg: use unix.Klogctl

Also remove the unused _SYSLOG_ACTION_READ const.

Signed-off-by: Tobias Klauser <9249c549618448e4c699e8032ba6c7f0d7fd4b7f@distanz.ch>

hugelgupf/u-root,hugelgupf/u-root,rminnich/u-root,rminnich/u-root,GanShun/u-root,u-root/u-root,hugelgupf/u-root,GanShun/u-root,GanShun/u-root,u-root/u-root,hugelgupf/u-root,u-root/u-root,rminnich/u-root,rminnich/u-root