Remove all event listeners on close to avoid memory leak

[jared-hexagon]

Summary

Fix for #805 by removing all event listeners on prompt.ui.close().

Testing

In the repro (https://github.com/jared-hexagon/inquirer-memory-leak-repro) I npm linked my fork and the MaxListenersExceededWarning warning never shows up.

[SBoudrias]

I'm not too sure about this change.

The problem is that we'll end up removing ALL listeners; even those that might've been setup outside of the Inquirer code base.

I'd prefer to specifically remove the listeners we're adding.

[jared-hexagon]

The problem is that we'll end up removing ALL listeners; even those that might've been setup outside of the Inquirer code base.

It only removes listeners for a single event emitter. If we create the emitter we should be safe to remove listeners for it (which we do in baseUI.js on line 15). Otherwise I think it will be a pain in the ass to remove each listener because of the layers going on.

[SBoudrias]

Yeah for sure won't be easy... Let's try this out, and if no one raises issues, we should be good to go.

[haoqunjiang]

#811
So this is causing bugs. Please revert.

[chrisdothtml]

In light of #811 I looked into this, and from what I can tell, this.rl is shared across all prompts. The readline instance is initially setup in lib/ui/baseUI.js:15, and the same instance (this.rl) is passed into all subsequent prompt instances created at lib/ui/prompt.js:85. So calling removeAllListeners removes listeners for all future prompts as well as the instance being closed.

I'm not too sure about this change...
...

Let's try this out, and if no one raises issues, we should be good to go

@SBoudrias in retrospect, perhaps a bit more scrutiny should be put on changes like this considering this package has 12mil+ weekly downloads

[jared-hexagon]

@chrisdothtml