Drop the vm_running global variable

Use runstate_is_running() instead, which is introduced by this commit.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
diff --git a/ui/sdl.c b/ui/sdl.c
index c7aaedf..8cafc44 100644
--- a/ui/sdl.c
+++ b/ui/sdl.c
@@ -409,7 +409,7 @@
     char icon_title[1024];
     const char *status = "";
 
-    if (!vm_running)
+    if (!runstate_is_running())
         status = " [Stopped]";
     else if (gui_grab) {
         if (alt_grab)
@@ -853,8 +853,8 @@
 {
     SDL_Event ev1, *ev = &ev1;
 
-    if (last_vm_running != vm_running) {
-        last_vm_running = vm_running;
+    if (last_vm_running != runstate_is_running()) {
+        last_vm_running = runstate_is_running();
         sdl_update_caption();
     }