refactor: replace the array for emitted values by the other sources on withLatestFrom

[Yozmo]

Replacing the hasValue array used to find whether or not the other sources have emitted. Using remainingValues which it's initialized with inputs.length and a boolean flag hasFirstValue (to find out if the current inner observable has emitted or not its first value) can easily replace the array.

[benlesh]

Hi @Yozmo — thank you for the time, care, and thoughtfulness you put into this pull request. I’m sorry we weren’t able to respond in a reasonable timeframe. Since the codebase and surrounding context have moved on and this hasn’t seen recent activity, I’m going to close it for now. That’s a reflection of our delayed triage, not a lack of appreciation for your contribution. If the change is still relevant, please feel welcome to open a fresh pull request against the current codebase. Thank you again for contributing to RxJS and for your patience.

— Ben