Remove maintainer mode

To quote from automake manual [1]:

    Several years ago François Pinard pointed out several arguments
    against this AM_MAINTAINER_MODE macro. Most of them relate to
    insecurity. By removing dependencies you get non-dependable builds:
    changes to sources files can have no effect on generated files and
    this can be very confusing when unnoticed. He adds that security
    shouldn't be reserved to maintainers (what --enable-maintainer-mode
    suggests), on the contrary. If one user has to modify a Makefile.am,
    then either Makefile.in should be updated or a warning should be
    output (this is what Automake uses missing for) but the last thing you
    want is that nothing happens and the user doesn't notice it (this is
    what happens when rebuild rules are disabled by AM_MAINTAINER_MODE).

[1] http://www.gnu.org/savannah-checkouts/gnu/automake/manual/html_node/maintainer_002dmode.html