Remove deprecated/unused context param (#851)

Author: ntre

React/Base/RCTTouchHandler.m

@@ -483,7 +483,7 @@ - (void)mouseDown:(NSEvent *)event
                                       modifierFlags:[event modifierFlags]
                                           timestamp:[event timestamp]
                                        windowNumber:[event windowNumber]
-                                            context:[event context]
+                                            context:nil
                                         eventNumber:[event eventNumber]
                                          clickCount:[event clickCount]
                                            pressure:[event pressure]];