Problem with exclude datasets in benchmark

[toncho11]

trafficstars

https://github.com/NeuroTechX/moabb/blob/ca79b9016ab99b4a76df882fdbb5d49da13106af/moabb/benchmark.py#L333

It seems if you have more than 1 excludes than the code indexing is no longer correct resulting in removing another dataset - not the desired one. This is because two lists datasets_codes and are no longer the same length and so the indexing becomes incorrect.

I will look into a solution now.