Revert D34645509: [PyTorch] Update Synchronized<T>::withLock() to return the type/value from the aceepted callable

Test Plan: revert-hammer

Differential Revision:
D34645509 (pytorch@de4a87f)

Original commit changeset: 9a4bd5d1d78a

Original Phabricator Diff: D34645509 (pytorch@de4a87f)

fbshipit-source-id: 3a1737cda866085fc0dec9997d0ce659f636a0c2
(cherry picked from commit 46d3300)

Author: suo

c10/util/Synchronized.h

@@ -42,9 +42,9 @@ class Synchronized final {
    * provided callback safely.
    */
   template <typename CB>
-  typename std::result_of<CB(T&)>::type withLock(CB cb) {
+  void withLock(CB cb) {
     std::lock_guard<std::mutex> guard(this->mutex_);
-    return cb(this->data_);
+    cb(this->data_);
   }
 
   /**
@@ -53,9 +53,9 @@ class Synchronized final {
    * the provided callback safely.
    */
   template <typename CB>
-  typename std::result_of<CB(T const&)>::type withLock(CB cb) const {
+  void withLock(CB cb) const {
     std::lock_guard<std::mutex> guard(this->mutex_);
-    return cb(this->data_);
+    cb(this->data_);
   }
 };
 } // end namespace c10