Remove "slave" terminology from illumos
The tricky part here is that we have committed interfaces in the DDI with the terms, e.g. ddi_slaveonly(9f). IMHO these should keep any interface names in header files and man pages (with history lessons). Other subsystems may be as easy as ZFS-via-OpenZFS, see #12851.
This may end up spawning smaller subsystem-specific bugs. We have 247 files hit.