Refactor Delistings Processing (#6059)

* Move processing of delistings to Brokerage

* Deal with case that exchange is not open on OptionSymbol.ID.Date

* Refactor solution to use DelistingNotification event

* Adjust some regression expected liquidation time

* Mark some todos on deprecated functions

* Update expected liqudation time for Py regressions

* Update regressions that have been validated

* Use HandlePositionAssigned for assignment orders

* Update regressions

* Update some missed unit tests; remove one that is already covered by regression

* Cleanup deprecated backend functions

* nit - small cleanup adjustment

* Post rebase fix

* Address review

* Minor tweak to py regression

Algorithm.CSharp/AddOptionContractExpiresRegressionAlgorithm.cs

@@ -139,8 +139,8 @@ namespace QuantConnect.Algorithm.CSharp
             {"Tracking Error", "0.049"},
             {"Treynor Ratio", "1.372"},
             {"Total Fees", "$2.00"},
-            {"Estimated Strategy Capacity", "$45000000.00"},
-            {"Lowest Capacity Asset", "AOL R735QTJ8XC9X"},
+            {"Estimated Strategy Capacity", "$67000000.00"},
+            {"Lowest Capacity Asset", "AOL VRKS95ENLBYE|AOL R735QTJ8XC9X"},
             {"Fitness Score", "0"},
             {"Kelly Criterion Estimate", "0"},
             {"Kelly Criterion Probability Value", "0"},
@@ -160,7 +160,7 @@ namespace QuantConnect.Algorithm.CSharp
             {"Mean Population Magnitude", "0%"},
             {"Rolling Averaged Population Direction", "0%"},
             {"Rolling Averaged Population Magnitude", "0%"},
-            {"OrderListHash", "b006bb7864c0b2f1a6552fb2aa7f03b8"}
+            {"OrderListHash", "4f50b8360ea317ef974801649088bd06"}
         };
     }
 }