fix linux-image-librem5 binary package

there is a bug with how linux-image-librem5 is created. It's created/installed just like the actual linux-image-6.3.0-1-librem5, but it should be an exception: It should contain nothing and exists only do have the "Depends" in d/control. deb-packaging scripts completely changed from v6.2..v6.3. Where should we best tweak them (probably scripts/package/builddeb ) to have an empty linux-image-librem5 again?