Partially MFC r345079 + direct commit to stable/11.

The MFC updates tools/build/mk/OptionalObsoleteFiles.inc.

The direct commit updates etc/rc.d/Makefile becasue this file was moved
in HEAD to libexec/rc/rc.d/Makefile, making svn merge impossible.

The original log message follows:

Fix still installing ipfilter rc.d files even when WITHOUT_IPFILTER
is specified.

When WITHOUT_IPFILTER is specified, delete-old-files fails to delete
the optional rc.d files from above. Fix this.

WITHOUT_IPFILTER fails to delete the ipfilter.5 optional file during
delete-old-files. Fix this.

Reported by: Dmitry Luhtionov <dmitryluhtionov@gmail.com>