configure: Stop using AM_MAINTAINER_MODE

AM_MAINTAINER_MODE can be used to disable generation of rebuild rules.
This is not something we want to condone/support, considering it can
cause greater problems than the perceived benefits. Additionally the
Automake manual leans towards avoiding the use of AM_MAINTAINER_MODE.

http://www.gnu.org/software/automake/manual/html_node/maintainer_002dmode.html



Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>