Remove %clean section

None of currently supported distributions need that.
Last one was EL5 which is EOL for a while.

Signed-off-by: Igor Gnatenko <ignatenkobrain@fedoraproject.org>

autoconf213.spec

@@ -83,9 +83,6 @@ if [ "$1" = 0 ]; then
     /sbin/install-info --delete %{_infodir}/%{name}.info %{_infodir}/dir || :
 fi
 
-%clean
-rm -rf ${RPM_BUILD_ROOT}
-
 %files
 %defattr(-,root,root,-)
 %{_bindir}/*