Kill AFS_64BIT_ENV

Kill AFS_64BIT_ENV

The AFS_64BIT_ENV was being pretty much universally defined. So,
remove the definition, and the conditional code that it controlled.
From this point on, all platforms are assumed to be capable of
handling 64bit values.

Change-Id: I3e4bde502af9f33f6998637c288e8fd0898ffa81
Reviewed-on: http://gerrit.openafs.org/2870
Tested-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>