Switch to using STAILQ_REMOVE_HEAD() instead of STAILQ_REMOVE_HEAD_UNTIL().

Submitted by: Stepan A. Baranov

This corresponds to OpenBSD rev. 1.134:

: revision 1.134
: date: 2004/05/04 16:59:31; author: grange; state: Exp; lines: +10 -10
: Remove useless ``elm'' argument from the SIMPLEQ_REMOVE_HEAD macro.
: This matches our SLIST behaviour and NetBSD's SIMPLEQ as well.
:
: ok millert krw deraadt