freebsd: changes necessary to coexist with dtrace in tree

Fix header conflicts when building zfs with openzfs as a vendor import.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes #10497

include/os/freebsd/spl/sys/condvar.h

@@ -35,7 +35,6 @@
 #include <sys/spl_condvar.h>
 #include <sys/mutex.h>
 #include <sys/time.h>
-#include <sys/kmem.h>
 
 /*
  * cv_timedwait() is similar to cv_wait() except that it additionally expects