Utterances can be removed from the queue as a side effect of Announcer.announce

[jessegreenberg]

See https://github.com/phetsims/joist/issues/752#issuecomment-1015639358. To reproduce, fuzz a sim that supports voicing and do not click into the simulation. Description of the stack that causes this:

• UtteranceQueue reaches attemptToAnnounce, we call voicingManager.announce. Since we haven't clicked in the simulation yet we get a SpeechSynthesisErrorEvent with error "not-allowed".
• This error immediately triggers the end event, and we call handleSpeechSynthesisEnd.
• This emits the endSpeakingEmitter.
• A listener on this Emitter in VoicingToolbarItem.js calls voicingManager.cancel() which eventually clears the UtteranceQueue.
• Then we continue in UtteranceQueue.attemptToAnnounce to try to remove the utterance from the queue even though the queue is empty.

I like the assertion in removeUtterance, but we need to be more graceful after calling attemptToAnnounce.

[jessegreenberg]

I believe this is fixed. @zepumph would you please review this change?

[zepumph]

Makes sense to me. Thanks for the quick turnaround!

[jessegreenberg]

Great, thanks.