package/libsigrok: drop remnants of autoreconf

package/libsigrok: drop remnants of autoreconf

libsigrok has not needed autoreconf since b428801934 (package/libsigrok:
bump version to 0.4.0), 4 years ago now.

As such, we no longer need the autoreconf options, nor the dependency on
the autoconf archive.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Bartosz Golaszewski <brgl@bgdev.pl>
Cc: Bernd Kuhls <bernd.kuhls@t-online.de>
Tested-by: Heiko Thiery <heiko.thiery@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>