Cache bypass: Remove AFS_KMAP_ATOMIC

Cache bypass: Remove AFS_KMAP_ATOMIC

Since AFS_KMAP_ATOMIC is defined unconditionally, remove the ifdefs
and the code for the !AFS_KMAP_ATOMIC case.  We probably don't want
to support this feature on a kernel old enough not to have kmap_atomic.
This should exist on all 2.6 and even 2.4 linux kernels.

This simplifies the code for maintenance and later changes.

Change-Id: I5d111d65066990123db917ac105a5a14db3b305f
Reviewed-on: http://gerrit.openafs.org/3372
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>