Remove empty Makefile continuation lines

HP-UX make gets confused by constructs like:

   FOO = bar \

   BAZ = quux

Where a line continuation is followed by an empty line. So, get rid of
all of these in the tree. Not all of them matter, but removing all of
them makes it easier to find these, and catch them in the future.

Reviewed-on: http://gerrit.openafs.org/7611
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Tested-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit 79f68de80e56179cfc5158fdcb51c34cfa864802)

Change-Id: Icf379b9d7557746c2c47134b1314a38ec13134cc
Reviewed-on: http://gerrit.openafs.org/8991
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Paul Smeddle <paul.smeddle@gmail.com>