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change is that the installation instructions are no longer current for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.

Author: elmiko

contributors/devel/sig-testing/e2e-tests.md

@@ -59,10 +59,9 @@ should also read [Writing Good e2e Tests](writing-good-e2e-tests.md)
 There are a variety of ways to run e2e tests, but we aim to decrease the number
 of ways to run e2e tests to a canonical way: `kubetest`.
 
-You can install `kubetest` as follows (If you face a download issue, please see issue [#14712](https://github.com/kubernetes/test-infra/issues/14712#issuecomment-541560441)):
-```sh
-go get -u k8s.io/test-infra/kubetest
-```
+For information on installing `kubetest`, please see the
+[installation section](https://github.com/kubernetes/test-infra/tree/master/kubetest#installation) of the
+[Kubetest project documentation](https://github.com/kubernetes/test-infra/tree/master/kubetest).
 
 You can run an end-to-end test which will bring up a master and nodes, perform
 some tests, and then tear everything down. Make sure you have followed the