doc: remove warning about scheduling interface being new and subject to change
The interface introduced in
1192654 (add isl_union_set_compute_schedule,
Sat Mar 19 14:47:47 2011 +0100) is not all that new anymore and
has already undergone some changes with the introduction of
schedule constraints in
74d4e1e (introduce new schedule API,
Wed Mar 21 14:32:26 2012 +0100) and the introduction of schedule trees
in
b0c84f7 (introduce schedule tree representation, Sun Jul 28 18:40:18
2013 +0200). The interface should now be fairly stable, at least not
less so than other parts of isl.
Signed-off-by: Sven Verdoolaege <skimo@kotnet.org>