Update AlphaStreamsBrokerageModel.cs
Update AlphaStreamsBrokerageModel.cs

Removes fixed leverage from the AS Brokerage Model. Inherits from the Default Brokerage Model.

jameschch/Lean,StefanoRaggi/Lean,StefanoRaggi/Lean,jameschch/Lean,jameschch/Lean,jameschch/Lean,jameschch/Lean,StefanoRaggi/Lean,JKarathiya/Lean,AlexCatarino/Lean,QuantConnect/Lean,AlexCatarino/Lean,QuantConnect/Lean,JKarathiya/Lean,JKarathiya/Lean,AlexCatarino/Lean,QuantConnect/Lean,JKarathiya/Lean,StefanoRaggi/Lean,AlexCatarino/Lean,StefanoRaggi/Lean,QuantConnect/Lean