Remove last "document not in toctree" warnings

Remove last "document not in toctree" warnings

There were two of them, for notice.rst and mitK5license.rst.
The former is included in the latter, which is linked to from
the mitK5features document but not listed in a table of contents
otherwise.  Includes are processed unconditionally, so we can
add notice.rst to the exclude_patterns array (formerly unused_docs)
and its content will still be included.

If we attempt to do the same for mitK5license.rst, it is not processed
at all, and the attempt to link to it will fail.  Instead, put a dummy
table of contents in the mitK5features document (which links to the
license document), with the "hidden" attribute.  This satisfies the
Sphinx need to know where all the input documents are without changing
the displayed table of contents.

ticket: 7447
tags: pullup
target_version: 1.11