Bug 1042642 - Remove eventSource from EnvironmentClient; r=jdescottes

After reviewing how the EnvironmentClient is used, it looks like the use of eventSource
might be some cruft from the past. Here is the try run:
https://treeherder.mozilla.org/#/jobs?repo=try&selectedJob=242251058&revision=df4bb52f188f79b8006e8c40401e5af2258493ce

with the exception of whatever is going on Window 7 (which appeares also on central), it looks like
things are working as expected. The environment client will eventually have the event emitter, once
it is moved to being a front.

adding @nchevobbe as a subscriber, as this touches a dependancy of the scratchpad.

Differential Revision: https://phabricator.services.mozilla.com/D28962

--HG--
extra : moz-landing-system : lando

devtools/shared/client/environment-client.js

@@ -5,7 +5,6 @@
 "use strict";
 
 const {arg, DebuggerClient} = require("devtools/shared/client/debugger-client");
-const eventSource = require("devtools/shared/client/event-source");
 
 /**
  * Environment clients are used to manipulate the lexical environment actors.
@@ -49,6 +48,4 @@ EnvironmentClient.prototype = {
   }),
 };
 
-eventSource(EnvironmentClient.prototype);
-
 module.exports = EnvironmentClient;