Revert "lib/modules: Pass credentials irrespective of "ExecProtocol"."

This reverts commit a72e70b4c45f109c6c9a434fd40131faa75b9eb8.

This change was incomplete.
Specifically, v.io/x/ref/lib/modules/exec.go does not pass in the connection to the agent to the subprocess if ExecProtocol is false.

It should be able to do that, I think. But I'll revisit that later.

Change-Id: Ib434900117b962e9262be8b7721ea0e2f5bf1fab
1 file changed