[Support] ThreadPoolExecutor: remove unused default argument

Author: MaskRay

llvm/lib/Support/Parallel.cpp

@@ -49,7 +49,7 @@ class Executor {
 ///   in filo order.
 class ThreadPoolExecutor : public Executor {
 public:
-  explicit ThreadPoolExecutor(ThreadPoolStrategy S = hardware_concurrency()) {
+  explicit ThreadPoolExecutor(ThreadPoolStrategy S) {
     ThreadCount = S.compute_thread_count();
     // Spawn all but one of the threads in another thread as spawning threads
     // can take a while.