Removed autogenerated gnulib files.

Leaving these files in the git-repo will break subdir builds, i.e.
the new files will be located in $subdir/gnulib, but the files in
$top_srcdir/gnulib will be used.

--

```make check && make distcheck``` complete successfully.

These files are already removed by ```make distclean``` (and recreated by ```make```), so should be safe to apply, but it's always nice if it's tested on more than one system (Ubuntu 12.04 LTS here).

 -- Simon