fix(fargate): start workers in parallel with lead task (#2459)

This reverts the behavior introduced in [1] where worker tasks
may wait for up to 60s whilst the lead task is preparing npm
dependencies.

The only benefit of waiting is to save up to 60s worth of
Fargate compute costs for tests where the lead task fails
to startup. This is rare.

Every test pays a penalty of having to wait for some time
for the lead task to be ready before the rest of the workers
even begin initializing however.

1. #2428

Author: hassy

packages/artillery/lib/platform/aws-ecs/legacy/run-cluster.js

@@ -1538,8 +1538,6 @@ async function launchLeadTask(context) {
     throw runErr;
   }
 
-  await awaitOnEE(context.reporterEvents, 'prepack_end', 1000 * 60 * 1);
-
   return context;
 }