configure.ac: Remove maintainer mode

Now that we no longer include generated files in our git repository
builds should always have maintainer mode enabled so checkouts pick
up on changes in Makefile.am, configure.ac, etc. between builds.

See #350.

configure.ac

@@ -11,10 +11,6 @@ AC_CONFIG_HEADERS([include/sane/config.h])
 
 AM_INIT_AUTOMAKE([1.15 subdir-objects -Wall])
 AM_SILENT_RULES
-dnl Turn off feature were automake will automatically run autoreconf.
-dnl This is because we used to check in generated files into CVS which
-dnl has known timestamp issues.
-AM_MAINTAINER_MODE
 
 dnl ******************************************************************
 dnl  Determine SANE version components and release status