OpenBSD: Remove macros definitions for afs_osi_Alloc et al.

OpenBSD: Remove macros definitions for afs_osi_Alloc et al.

The afs_osi_Alloc, afs_osi_Free, etc. routines are now
defined in afs_osi_alloc.c so the macro definitions defined
by osi_machdep.h for OpenBSD are no longer needed and, in
fact, interfere with the compile. Remove them.

Change-Id: I98a261b5cd5e44136e4dde677f86d90212b0cfba
Reviewed-on: http://gerrit.openafs.org/3681
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>