issue a pytest-waring on eol and known to be broken python versions

[RonnyPfannschmidt]

after crosschecking with some of our users i realized we should sync our policy with pip

however its reasonable to warn users of python2.6 that their python is eol
the same holds true for 3.0 and 3.1, 3.2 will join in february

this is a followup to #1273

[The-Compiler]

I don't think this should be pytest's job. If I was using those python versions, it sure would get me to never look at pytest warnings again.

[nicoddemus]

I kind of agree with @The-Compiler as well... people already kind of dislike pytest-warnings because most of the time the users can't do anything about them (for example in an external plugin).

I think we could just make that clear during the release announcements for 2.9 and onward that we will drop 2.6 as soon as pip does.

[RonnyPfannschmidt]

I agree, closing as wont fix