get rid of minimum-[XY]-extents (issue 6294086)

[k-ohara5a5a]

Nobody told me minimum-*-extents were deprecated, except for their use
in staff-spacing, so I have been using and recommending them.
http://lists.gnu.org/archive/html/lilypond-user/2011-11/msg00217.html
http://lists.gnu.org/archive/html/lilypond-user/2011-07/msg00427.html

The docstring for X-extent says it is "hard-coded" so I didn't think I
was allowed to change them.  The minimum-*-extent is convenient when you
want extra space on one side, and don't want to think about what extent
the object should have on the other side.


http://codereview.appspot.com/6294086/diff/1/lily/grob.cc
File lily/grob.cc (left):

http://codereview.appspot.com/6294086/diff/1/lily/grob.cc#oldcode484
lily/grob.cc:484: SCM min_ext = get_property ("minimum-Y-extent");
Removing this is a good idea, because staff spacing no longer treats
Y-extents in a special way.

http://codereview.appspot.com/6294086/diff/1/scm/define-grob-properties.scm
File scm/define-grob-properties.scm (left):

http://codereview.appspot.com/6294086/diff/1/scm/define-grob-properties.scm#oldcode279
scm/define-grob-properties.scm:279: (extra-X-extent ,number-pair? "A
grob is enlarged in
These properties have no effect, so it would be good to remove their
docstrings.
http://lists.gnu.org/archive/html/lilypond-user/2009-01/msg01154.html

http://codereview.appspot.com/6294086/diff/1/scm/define-grob-properties.scm#oldcode964
scm/define-grob-properties.scm:964: (X-extent ,number-pair? "Hard coded
extent in address@hidden")
Maybe "Extent in the X-direction, measured in staff-space units."

http://codereview.appspot.com/6294086/