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

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>
(cherry picked from commit 675bd1007de6594321c03d6f92261f909120643f)

Change-Id: I9706a4d05044740fc6bb700fc5f1ef92923ce4bf
Reviewed-on: http://gerrit.openafs.org/5389
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>