systemd: ditch autoreconf

It needs AM_PATH_LIBGCRYPT and will bail out if ALL_EXTRAS (libgcrypt)
isn't around - and it doesn't seem to be used at all.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>