BufferedSink: Remove progress notifications

[jsor]

This PR removes triggering progress notifications on the promise returned by BufferedSink.

I always recommend to avoid the progression API of promises (it's underspecified, has subtle problems and has little to do with promises).

If you need to listen on data events, use the ReadableStream directly.

[WyriHaximus]

LGTM 👍 && +1

[clue]

LGTM 👍

For the reference: See reactphp/promise#32 for some background

[clue]

I think we all agree that we want to remove the promise progression API and getting this in is the right thing to do 👍

However, this currently targets the v0.4.4 milestone and dropping this feature ought to be considered a BC break. This means we would have to move this (and all following PRs) to a future v0.5.0 milestone.

As such, my vote would be to revert this PR for now so that we get the other changes out. We should reconsider this for the v0.5.0 release. /cc @cboden, @jsor, @WyriHaximus

[jsor]

Oh yes, i wasn't aware this has already been merged. 👍 for reverting.

[clue]

For the reference: This has been reverted via #44 and will not end up in any release.

#45 will likely remove the whole class in the next major release.