Back out "[flipper] disconnect client instead of removing it"
Back out "[flipper] disconnect client instead of removing it"

Summary:
Original commit changeset: 650ef1344b8b

Backing this out until we can come up with a better way to do it.

The change was introduced so that when a device disconnects / crashes, we don't lose all plugin state, and you can still see what was on screen before the crash..

However, there are some problems with this solution, which get quite complicated. Putting them here for future reference:
* Closing an app results in the plugins staying there, and there's no way to tell it's not actually connected.
* If the app reconnects, the JS plugin doesn't get re-initialized. Even though the client plugin has been.

Reviewed By: bnelo12

Differential Revision: D16280931

fbshipit-source-id: 48e09b876e631aa87372054e706cdb9a2b3e2eb7

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