queue.h: Define {LIST,TAILQ}_REMOVE_HEAD

The LIST and TAILQ structures have fast _REMOVE macros (since each
element has a pointer to the previous element); we implement the
_REMOVE_HEAD macros for them by simply finding the first element and
then removing it.

Reviewed by: jhb, emaste
Sponsored by: https://www.patreon.com/cperciva
Differential Revision: https://reviews.freebsd.org/D41072