Move deprecation of SWEET32/64bit block size ciphers to 2.7

Move deprecation of SWEET32/64bit block size ciphers to 2.7

We originally wanted to deprecated these ciphers (especially BF-CBC) with
2.6 but currently these ciphers are still too widespread to make this
transition for 2.6.

Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20211213150950.3993881-1-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg23402.html

Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 7f2d7dbf986fd7233eabb250b35bf7c3112d3e37)