Deprecation of SSL v2/3

[Phil Sorber]

I'd like to propose that we deprecate SSLv2 and SSLv3 in ATS 6.2.0 and
remove it in 7.0.0.

Currently our defaults do not enable them and have been that way for about
a year now. For 6.2.0 I'd like to mark them deprecated in the
documentation, and then we remove the code for 7.0.0. This will mean that
as of 7.0.0 you will not be able to enable SSLv2/3 even if your OpenSSL
library supports it.

Appreciate any feedback.

Thanks.