Remove option --nix* on run-webkit-tests because there's no nix-wk2, etc, only nix.

Reviewed by: Marcelo Lira
Remove outdated comments and unused functions.

Reviewed by: Marcelo Lira
Remove our changes on webkitpy/port/base.py and implement then directly on NixPort class.

This patch also add the wk2 directory to the TestExpectations search path.

Reviewed by: Marcelo Lira
Make Tools/Scripts/test-webkitpy pass again after changes in TestExpectation search paths and reverts on port_testcase.py.

Reviewed by: Marcelo Lira