Remove AsyncCall.h

None of the function in AsyncCall are in use anymore so we can delete
it. This contained code for implementing swift asynchronous functions in
C++.

Author: etcwilde

stdlib/public/Concurrency/AsyncCall.h

@@ -24,7 +24,6 @@
 #include "swift/Runtime/HeapObject.h"
 #include "llvm/ADT/PointerIntPair.h"
 #include "TaskPrivate.h"
-#include "AsyncCall.h"
 #include "Debug.h"
 
 #if !defined(_WIN32)

stdlib/public/Concurrency/AsyncLet.cpp

@@ -24,7 +24,6 @@
 #include "swift/Runtime/HeapObject.h"
 #include "TaskGroupPrivate.h"
 #include "TaskPrivate.h"
-#include "AsyncCall.h"
 #include "Debug.h"
 #include "Error.h"
 

stdlib/public/Concurrency/Task.cpp

@@ -28,7 +28,6 @@
 #include "swift/Runtime/Config.h"
 #include "swift/Runtime/Mutex.h"
 #include "swift/Runtime/HeapObject.h"
-#include "AsyncCall.h"
 #include "Debug.h"
 #include "bitset"
 #include "string"