MFC r250951,251838:

Ensure alq's shutdown_pre_sync event handler is deregistered on module unload to
avoid a dangling pointer and eventual panic on system shutdown.

Reported by:	Ali <comnetboy at gmail.com>
MFC r251682:

Remove some duplicate code by making KHELP_DECLARE_MOD() a wrapper around
KHELP_DECLARE_MOD_UMA().