Remove unused dependency on optional from ParkingLot

Summary: as title

Reviewed By: yfeldblum

Differential Revision: D14476923

fbshipit-source-id: 5ce16adb2402720b16acd12ab0003c1e93395f6c

folly/synchronization/ParkingLot.h

@@ -21,7 +21,6 @@
 
 #include <folly/Hash.h>
 #include <folly/Indestructible.h>
-#include <folly/Optional.h>
 #include <folly/Portability.h>
 #include <folly/Unit.h>
 #include <folly/lang/SafeAssert.h>

folly/synchronization/test/AtomicNotificationTest.cpp

@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 #include <folly/synchronization/AtomicNotification.h>
+
+#include <folly/Optional.h>
 #include <folly/portability/GTest.h>
 
 #include <thread>