DARWIN: replace macro exported by automake

DARWIN: replace macro exported by automake

Commit 4706854f57043c8393baa922dd1974176e110a19 removed automake
references from the source tree. As a result, VERSION (exported by
AM_INIT_AUTOMAKE and obtained from Autoconf's AC_INIT macro) is not
available anymore. Unfortunately, a reference to this macro can be found
in src/afs/DARWIN/osi_module.c. Consequently, builds on OS X fail with
the following message:

    osi_module.c:144:32: error: use of undeclared identifier 'VERSION'

To fix this problem, replace VERSION by PACKAGE_VERSION (defined by
AC_INIT).

Change-Id: Ib3821d79c4cddd59c399985762e13dec755d8642
Reviewed-on: https://gerrit.openafs.org/13354
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>