These have been detach from build for long time.
Removing these as a part of sys/sys/inflate.h removal.
It looks this change hasn't yet committed.
Could you hold on to this for a while?
I found https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=183666 and it looks kgzip was working until 8.4 release which is much newer release than I had found. I'd like to spend more time to find how to set it and and if this still works.