www/speedtest-mini: Set DEPRECATED (2017-06-30, Discontinued)

Upstream has announced [1] the discontinuation of speedtest-mini:

As of June 30, 2017 Speedtest Mini will no longer be available, and all
current licenses will expire. We encourage you to upgrade to Speedtest
Custom for free at your earliest convenience.

Accordingly, set DEPRECATED and mark port EXPIRATION_DATE 2 months from
discontinuation date (30th August, 2017).

[1] http://www.speedtest.net/mini.php

PR: 220029
Submitted by: Koichiro IWAO <meta+ports vmeta jp> (maintainer)
MFH: 2017Q3