Investigate `_patch_vcr_from_serialized_response` and remove if possible

[ramnes]

I merged the _patch_vcr_from_serialized_response function (in conftest) with PR #270 because I didn't have much time to investigate this function, and because the potential impact seemed very low. But I think it looks overly complex, and probably means there is something we need to fix upstream or something we do wrong here. Let's investigate and see if we can remove it or if we can make something simpler!