Staff.VerticalExtent in lilypond 2.4.0?

[Dominik Baenninger]

In earlier versions of lilypond (e.g. 2.2.6) I reduced the space between
the staffs with

\score {
   << \set Staff.minimumVerticalExtent = #'(-1 . 1 )
      \set Staff.VerticalExtent = #'(-1 . 1 )
      \hornOneNotes>>}

>From the manual of 2.4.0 I learned that Staff.VerticalExtent does not
exist anymore. In which way can I reduce spaces between staffs? If I use

score {
   << \set Staff.minimumVerticalExtent = #'(-1 . 1 )
      \hornOneNotes>>}

As the manual says, then I can only increase but not decreas the space
between the staffs.

Has anyone an idea?

Dominik