Core: Hide determinism global

This is only ever queried and not set outside of the Core.cpp, so this
should just be hidden internally and just have a function exposed that
allows querying it.

Source/Core/Core/Core.h

@@ -21,8 +21,6 @@ namespace Core
 // TODO: ugly, remove
 extern bool g_aspect_wide;
 
-extern bool g_want_determinism;
-
 bool GetIsThrottlerTempDisabled();
 void SetIsThrottlerTempDisabled(bool disable);
 
@@ -51,6 +49,8 @@ bool IsRunningInCurrentThread();  // this tells us whether we are running in the
 bool IsCPUThread();               // this tells us whether we are the CPU thread.
 bool IsGPUThread();
 
+bool WantsDeterminism();
+
 // [NOT THREADSAFE] For use by Host only
 void SetState(State state);
 State GetState();