From Christoph Hellwig <hch@lst.de>

If we're ever going to ressurect umsdos it should be a stackable
filesystem..

One of the goals of the whole new modversions implementation:
export-objs is gone for good!

Makefiles no longer need to include Rules.make, which is currently an
empty file.  This patch removes it from the remaining Makefiles, and
removes the empty Rules.make file.