update kubetest installation instructions in the developer e2e testing documentation
update kubetest installation instructions in the developer e2e testing documentation

This change removes the installation instructions for kubetest
in favor of links to the project documentation. The reason for this
change is that the installation instructions are no longer current for
the project, this removal will aid with a de-duplication of information.

kubernetes/community,pwittrock/community,kubernetes/community,pwittrock/community,kubernetes/community