XQuartz: Rever the "Set can_quit to true during a Sparkle-initiated relaunch." change

This was in place to work around the issue that was correctly solved with the
previous commit (changing the Windows menu behavior).  Reverting this change
no longer causes crashing, so it's safe to show the dialog now.
(cherry picked from commit 023cef31bb)

hw/xquartz/X11Controller.m

@@ -343,7 +343,7 @@ BOOL xquartz_resetenv_display = NO;
 
 // Sent immediately before installing the specified update.
 - (void)updater:(SUUpdater *)updater willInstallUpdate:(SUAppcastItem *)update {
-    [self set_can_quit:YES];
+    //[self set_can_quit:YES];
 }
 
 #endif