[autotools] Remove second call to AM_INIT_AUTOMAKE.

Complained by autoconf 1.14, cf. FS#1462.

(cherry picked from commit 50c83dc45922cbe8ae0e8b36711068696f6c256e)
Signed-off-by: Christoph Grüninger <gruenich@dune-project.org>
Actually return 3-dim simplex when dim=3

Cc: Katja Hanowski <hanowski@igpm.rwth-aachen.de>
(cherry picked from commit 03408fa565fe5ddd87a9edfb506c6c5b18368755)
Signed-off-by: Christoph Grüninger <gruenich@dune-project.org>