Now that FreeBSD 9.3, 10.1, and 10.2 have are no longer supported, remove
their links from the front and download page and the side bar.

Move these releases to the list of past releases and mark them as
"not officially supported".

Do not remove the entities for these releases as they are still used in
other parts of the documentation.

Submitted by: rene
Approved by: re (gjb)
Differential Revision: https://reviews.freebsd.org/D9018