LU-2675 cleanup: remove User Mode Linux specific code

The UML specific code has been uncompilable for some time and no one
has complained so it goes.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: Ie91c6e4484fee64fec4a2e38effd8a1021e8cddb
Reviewed-on: http://review.whamcloud.com/5175


Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>