Remove obsolete parts of autoconf_inc.m4.

This file has accumulated a lot of condition checks which were not relevant
any more, remove and recreate it (by running bakefile_gen) to get rid of them.

Closes #15101.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73648 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775