[TypeCheckConcurrency] Stop exposing isAsynchronousContext as no longer useful

`ConstraintSystem` has its own method to determine this.

Author: xedin

lib/Sema/TypeCheckConcurrency.cpp

@@ -1744,7 +1744,21 @@ namespace {
     }
 
     bool isInAsynchronousContext() const {
-      return isAsynchronousContext(getDeclContext());
+      auto *dc = getDeclContext();
+
+      if (auto func = dyn_cast<AbstractFunctionDecl>(dc)) {
+        return func->isAsyncContext();
+      }
+
+      if (auto closure = dyn_cast<AbstractClosureExpr>(dc)) {
+        if (auto type = closure->getType()) {
+          if (auto fnType = type->getAs<AnyFunctionType>()) {
+            return fnType->isAsync();
+          }
+        }
+      }
+
+      return false;
     }
 
     enum class AsyncMarkingResult {
@@ -4193,22 +4207,6 @@ bool swift::completionContextUsesConcurrencyFeatures(const DeclContext *dc) {
   return contextUsesConcurrencyFeatures(dc);
 }
 
-bool swift::isAsynchronousContext(const DeclContext *dc) {
-  if (auto func = dyn_cast<AbstractFunctionDecl>(dc)) {
-    return func->isAsyncContext();
-  }
-
-  if (auto closure = dyn_cast<AbstractClosureExpr>(dc)) {
-    if (auto type = closure->getType()) {
-      if (auto fnType = type->getAs<AnyFunctionType>()) {
-        return fnType->isAsync();
-      }
-    }
-  }
-
-  return false;
-}
-
 AbstractFunctionDecl const *swift::isActorInitOrDeInitContext(
     const DeclContext *dc,
     llvm::function_ref<bool(const AbstractClosureExpr *)> isSendable) {

lib/Sema/TypeCheckConcurrency.h

@@ -329,10 +329,6 @@ bool isDispatchQueueOperationName(StringRef name);
 bool checkSendableConformance(
     ProtocolConformance *conformance, SendableCheck check);
 
-/// Check whether the given declaration context is asynchronous e.g.
-/// function or a closure declaration marked as `async`.
-bool isAsynchronousContext(const DeclContext *dc);
-
 /// Check whether we are in an actor's initializer or deinitializer.
 /// \returns nullptr iff we are not in such a declaration. Otherwise,
 ///          returns a pointer to the declaration.