Bug 35713: Remove outdated debian/docs/LEEME.Debian file

Bug 35713: Remove outdated debian/docs/LEEME.Debian file

This removes the LEEME.Debian README file from the docs
directory. We don't even have an English README here as
we usually refer to the wiki for installation instructions.
It makes sense to remove it from the codebase.

To test:
* Verify that the file is removed
* Verify that all references to the file have been removed as well
  Example: git grep LEEME

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>