afsio: remove unnecessary reference to malloc.h

afsio: remove unnecessary reference to malloc.h

Fixes breakage on freebsd for missing malloc.h, reported by GAWollman,
and, since roken.h already includes stdlib.h to pull in malloc, is no
longer necessary

Change-Id: Ie7785198124fe0dee394d7c15f032f0dadb6db8c
Change-Id: I1d5947155ba33de61d8fd23197e11c51e4791935
Reviewed-on: http://gerrit.openafs.org/4578
Reviewed-by: Chaz Chandler <clc31@inbox.com>
Tested-by: Chaz Chandler <clc31@inbox.com>
Reviewed-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Reviewed-by: Derrick Brashear <shadow@dementia.org>