Remove Servlet 2.5 Support for Session Fixation

[jzheaux]

Related to #6220

There are a couple of different strategies available to users for performing session fixation. One such, ChangeSessionIdSessionAuthenticationStrategy, requires a method only available on HttpServletRequest since Servlet 3.1.

Because of this, its constructor checks for the existence of that method and throws an exception otherwise.

Now that the Spring Framework baseline is Servlet 3.1, that check is no longer necessary.

Also, the corresponding try/catch in
SessionManagementConfigurer and the corresponding conditional in HttpConfigurationBuilder are no longer necessary.

Of course, this also means that tests that confirm this behavior can also be removed.

[raphaelDL]

I will take this I'm taking this

[rwinch]

Thanks the issue is yours @raphaelDL!