update code to remove ex variable

Author: Harini Malothu

vnext/Mso/src/dispatchQueue/threadPoolScheduler_win.cpp

@@ -279,7 +279,7 @@ ThreadPoolSchedulerWin *ThreadPoolSchedulerWinContext::CurrentScheduler() noexce
 
     // Return the scheduler if everything is good
     return scheduler;
-  } catch (const std::exception& ex) {
+  } catch (const std::exception&) {
     // Catch any exceptions from Verify and return nullptr
     return nullptr;
   }