Remove empty Makefile continuation lines

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.

Change-Id: I7d5ef000b5b55de4b71c183589fbfe36e3880ba1
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>