s390: desupport 32-bit Linux kernels on s390/s390x

s390: desupport 32-bit Linux kernels on s390/s390x

Remove the obsolete and custom lwp assembler for the s390 and s390x
architectures.  That assembler is no longer needed since 32-bit
mainframe Linux distributions are no longer supported and are very
unlikely to be in use.

The generic process.default.s is sufficient for modern 64-bit Linux
distributions on s390/s390x.

[mmeffie@sinenomine.net: commit message wording]

Reviewed-on: https://gerrit.openafs.org/12475
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit 1d8cb56999a4ab25ae4cbc8e8a688b8100aedd3b)

Change-Id: Iee572ef3a86f5502e37ddc0775da13b874add669
Reviewed-on: https://gerrit.openafs.org/12499
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>