Fix memory leak in MapLoadEvent

[kamil-sienkiewicz-asi]

Hey @stepankuzmin, as promised there is my PR fixing memory leak in mapbox. Right now whole Map is being cleaned when it's unmounted.

That's actually pretty funny how this line

postMapLoadEvent(this._getMapId(), this._requestManager._skuToken, this._requestManager._customAccessToken, () => {});

caused memory leak, function () => {} passed as error callback has access to this which is actually a Map object. Function was never cleaned therefore it was holding everything alive :D To my understanding any definition of function like so:

function errCb(){}

postMapLoadEvent(this._getMapId(), this._requestManager._skuToken, this._requestManager._customAccessToken, errCb);

would also leak as errCb also has indirect access to whatever is in _authenticate function which ultimately holds this.painter.context.gl but that's something I'm not sure about.

Hope it makes sense 💯

[mourner]

Looks good to me! Alternatively we could also modify the postMapLoadEvent code so that it doesn't accept a callback since it's completely unused, but not sure about this — @stepankuzmin do we want to possibly handle errors properly here in the future?

[stepankuzmin]

Excellent, thanks for shipping this, @kamil-sienkiewicz-asi!

@mourner I think we should be safe to delete unused callback, as we don't have plans to handle those errors. However, we should discuss it before removing it, so I think we could merge this and get back to it later 👍