[Sema] NFC: Remove shouldWalkIntoClosure

This used to have some logic when multi-statement
closures were type-checked differently, it's always
true now.

Author: hamishknight

lib/Sema/TypeCheckAvailability.cpp

@@ -3721,10 +3721,8 @@ class ExprAvailabilityWalker : public ASTWalker {
                                CE->getResultType(), E->getLoc(), Where);
     }
     if (AbstractClosureExpr *closure = dyn_cast<AbstractClosureExpr>(E)) {
-      if (shouldWalkIntoClosure(closure)) {
-        walkAbstractClosure(closure);
-        return Action::SkipChildren(E);
-      }
+      walkAbstractClosure(closure);
+      return Action::SkipChildren(E);
     }
 
     if (auto CE = dyn_cast<ExplicitCastExpr>(E)) {
@@ -3952,10 +3950,6 @@ class ExprAvailabilityWalker : public ASTWalker {
     walkInContext(E->getSubExpr(), accessContext);
   }
 
-  bool shouldWalkIntoClosure(AbstractClosureExpr *closure) const {
-    return true;
-  }
-
   /// Walk an abstract closure expression, checking for availability
   void walkAbstractClosure(AbstractClosureExpr *closure) {
     // Do the walk with the closure set as the decl context of the 'where'