there are insque() and remque() defined at the end (under an xxx comment, which states that they are the old way of doing things). Their only user appears to be netipx/spx_usrreq.c.
My bet is that no one is going to tackle the ipx code, so the need for the two will last for as long as the ipx code exists. And the xxx in sys/queue.h will poke in the eye for a long time.
I propose to move the xxx part of sys/queue.h to a private netipx header (e.g. Netipx/_queue.h).
Patch will follow, if the idea is considered worthwhile.