configure.ac: don't use internal GNU libtool functions

This doesn't work when using slibtoolize instead of GNU libtoolize and
is not necessary anyways.

Signed-off-by: orbea <orbea@riseup.net>

configure.ac

@@ -27,7 +27,6 @@ AM_INIT_AUTOMAKE([foreign no-define])
 AM_MAINTAINER_MODE([enable])
 
 AC_CANONICAL_HOST
-_LT_SET_OPTION([LT_INIT],[win32-dll])
 LT_INIT
 
 AC_C_BIGENDIAN