libtorrent: remove manual autoconf invocation

libtorrent: remove manual autoconf invocation

The Makefile already uses the proper autoreconf fixup but leaves a manual
autoconf invocation in place.

The bad autoconf call leads to the following build error in the SDK:

	configure.ac:3: installing `./config.guess'
	configure.ac:3: installing `./config.sub'
	configure.ac:20: installing `./install-sh'
	configure.ac:20: installing `./missing'
	src/Makefile.am: installing `./depcomp'
	autoreconf: Leaving directory `.'
	aclocal...
	autoheader...
	libtoolize... libtoolize nor glibtoolize not found
	make[2]: *** [.../.configured_] Error 1

Remove the entire Build/Configure override to let libtorrent build correctly.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>