* automake.in (@common_files): Remove acinclude.m4 since

* automake.in (@common_files): Remove acinclude.m4 since
it will be m4_included by aclocal.m4 and files are always
distributed.
(scan_aclocal_m4): Do not bother about acinclude.m4 anymore.
We will get this dependency when tracing m4_includes.
* tests/aclocal6.test: Make sure acinclude.m4 is distributed
when used.
* tests/acinclude.test: Delete.
* tests/Makefile.am (TESTS): Remove acinclude.test.