project.conf: No need to customize the "autogen" variable on autotools
This is now the default behaviour in buildstream since buildstream commit 8f2bf4e6e97f3ff859653c6cf60010ce9a2ebca0
Part of #300
Edited by Javier Jardón
This is now the default behaviour in buildstream since buildstream commit 8f2bf4e6e97f3ff859653c6cf60010ce9a2ebca0
Part of #300