sdl: prevent simulator build from using pthreads

The simulator build will pull in the host SDL headers, which we can't
filter out easily. A simple workaround is to simply remove the pthread
include from our SDL.

Change-Id: I09de0f2e85b891aa88958e21426ab450af516e76
diff --git a/apps/plugins/sdl/src/thread/SDL_thread_c.h b/apps/plugins/sdl/src/thread/SDL_thread_c.h
index 9534c8a..d0804e9 100644
--- a/apps/plugins/sdl/src/thread/SDL_thread_c.h
+++ b/apps/plugins/sdl/src/thread/SDL_thread_c.h
@@ -35,8 +35,6 @@
 #include "os2/SDL_systhread_c.h"
 #elif SDL_THREAD_PTH
 #include "pth/SDL_systhread_c.h"
-#elif SDL_THREAD_PTHREAD
-#include "pthread/SDL_systhread_c.h"
 #elif SDL_THREAD_SPROC
 #include "irix/SDL_systhread_c.h"
 #elif SDL_THREAD_WIN32