This is my first ever patch touching ExprEngine, sorry if the code causes lasting damage to the reader.
One of the pain points in simplifying MallocCheckers interface by gradually changing to CallEvent is that a variety of C++ allocation and deallocation functionalities are modeled through preStmt<...> where CallEvent is unavailable, and a single one of these callbacks can prevent a mass parameter change.
This patch introduces a new CallEvent, CXXDeallocatorCall, which happens after preStmt<CXXDeleteExpr>, and can completely replace that callback as demonstrated. Note how you can retrieve this call through preCall, yet there is no postCall to pair it with -- the reason behind this is that neither does preStmt<CXXDeleteExpr> have a postStmt<CXXDeleteExpr> pair. But I have no clue why that is :^)