Sayōnara, AM_MAINTAINER_MODE!

If --enable-maintainer-mode got lost from config.status for any reason,
builds would fail in mysterious ways after changing between different
Git commits.

There are more reasons for dropping it in the automake manual:

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

I'm not aware of any reason why --disable-maintainer-mode would ever be
useful with this project.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
(Cherry picked from radeon commit 49cf3b5032a7ce40afe514b7092440e3e19e05aa)

autogen.sh

@@ -10,5 +10,5 @@ autoreconf -v --install || exit 1
 cd $ORIGDIR || exit $?
 
 if test -z "$NOCONFIGURE"; then
-    $srcdir/configure --enable-maintainer-mode "$@"
+    $srcdir/configure "$@"
 fi

configure.ac

@@ -36,8 +36,6 @@ AC_CONFIG_AUX_DIR(.)
 AM_INIT_AUTOMAKE([foreign dist-bzip2])
 AC_SYS_LARGEFILE
 
-AM_MAINTAINER_MODE
-
 # Require X.Org macros 1.8 or later for MAN_SUBSTS set by XORG_MANPAGE_SECTIONS
 m4_ifndef([XORG_MACROS_VERSION],
           [m4_fatal([must install xorg-macros 1.8 or later before running autoconf/autogen])])