autogen.sh: remove aclocal calls, not needed anymore

Since we stop using autoconf macros (such as PKG_CHECK_MODULES;
see [1]) in [2], aclocal is not likely to be needed anymore.

[1] http://tirania.org/blog/archive/2012/Oct-20.html
[2] https://github.com/fsharp/fsharp/commit/cded42fb1929f9ca1edcb5ecc38c052287caba0e