Change how the upstream tarball is generated

Change how the upstream tarball is generated

* Upstream no longer includes files covered by the Apple Public Source
  License, so we no longer have to repackage the upstream source to
  remove those files.  Drop Debian patches to the build system that were
  compensating for the removal of those files.
* Switch to generating upstream tarballs from the upstream Git tag
  rather than from tarball releases.  There's no reason to include all
  the generated files when we're going to regenerate them anyway, and
  this saves effort combining the doc and src tarballs.