Retire Makefile.shared

It has served its purpose, and been replaced by libtool.

Change-Id: Ifb4e2f585fb4239e9138daef82dcc7f41d7f2a99
Reviewed-on: http://gerrit.openafs.org/11485
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: D Brashear <shadow@your-file-system.com>
Merge pam into the kauth configure option

Realistically, you shouldn't be using either kauth or pam.  The
pam functionality provided by the module in our tree is only
useful in a kaserver-style environment, so it makes sense to merge
the two knobs.

Retain a separate enable_pam variable so that it can be overridden
on a per-architecture basis where it is known to not work.  Consolidate
the two places where we did such checks, as well.

Change-Id: I6bf39ee5002f943548c51d089fe612f7e2f0501b
Reviewed-on: http://gerrit.openafs.org/11524
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: D Brashear <shadow@your-file-system.com>