Don’t remove the just set asset

It doesn’t help anything, and is in fact confusing, because 1) the field will show up anyway the next time attributesChanged is called, and 2) it doesn’t match our docs in which we say that the field will be there.
Update docs to better describe `attribute` in `playerApi.requestAsset`
Merge pull request #18 from Versal/dont-remove-asset-field

Dont remove asset field