Remove native methods not used by jansi

[gnodet]

Jansi 2.3.0 introduced 2 native methods (setenv and chdir) which are used by https://github.com/mvndaemon/mvnd but not jansi, so they should be removed once apache/maven-mvnd#400 has been released.

[davsclaus]

@gnodet has that mvnd been released? If so then this ticket can be implemented

[gnodet]

Yes, definitely, I'll get rid of those two methods.