rsyslog: drop autoreconf

The patches touching configure.ac were dropped in 9d9bbf9b (rsyslog: bump
to version 8.8.0, 2015-02-25). Remove autoreconf as well.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>