afs_snprintf is dead, long live rk_snprintf

afs_snprintf is dead, long live rk_snprintf

We were shipping our own implementation of snprintf and friends, as
afs_snprintf. Now that we're using roken everywhere, we can make use
of roken's rk_snprintf, and no longer need to ship our own.

As Window's snprintf isn't C99 compliant, roken always uses its own
on this platform. The effect of this is that we can no longer use
AFS_UINT64_FMT and AFS_INT64_FMT for snprintf calls (and the Log
functions that call them). Instead, we need to always use the
Unix format specifiers when calling these functions.

Make thse changes across the whole tree.

Change-Id: I3fffef97566f239ad639f15c4decd136d5bbd765
Reviewed-on: http://gerrit.openafs.org/4316
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>