Stop re-creating EventSources upon receiving a close event

[Shaptic]

Context: #567. In that PR, the SDK was updated to handle the event: close event as well as recreate the EventSource object when the event occurred to keep the stream open.

However, according to the MDN documentation on server-side events:

By default, if the connection between the client and server closes, the connection is restarted. The connection is terminated with the .close() method.

Now, it's unclear if the above became spec'd behavior after #567 or not, but the point is, it appears we no longer need to recreate the event stream. Doing so causes test failures such as this one:

  1) integration tests: streaming
       handles close message:
     Error: done() called multiple times
      at IncomingMessage.<anonymous> (test/integration/streaming_test.js:51:9)
      at IncomingMessage.emit (node:events:526:28)
      at emitCloseNT (node:internal/streams/destroy:138:10)
      at processTicksAndRejections (node:internal/process/task_queues:82:21)

This is likely because the call builder is recreating the event stream on the close, making it close twice.

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(Adding reviewers from #567.)

[acharb]

lgtm!
seems odd that the error just shows up in the test now though, @Shaptic any idea why that is? (or is it an irregular error that pops up occasionally)

[Shaptic]

@acharb I've only seen it in browser tests when using Node 16 (and then, only semi-consistently, I think...) 🕵️ but now it's happening consistently since Node 16 is in the test matrix...