debian/nxproxy.docs: Fix FTBFS due to missing documentation files (moved out of the way with recent commits).

  The installation process copies NX wrapper scripts into
  $(srcbase)/bin/ before build time.

  Those wrapper scripts are now in place natively and need not
  to be copied prior to building NX.

  Packaging scripts with adaptation:

   debian/roll-tarballs.sh
   debian/rules
   debian/*.docs
   nx-libs.spec