core: core_timing: Remove unused IsHostTiming.

src/core/core_timing.h

@@ -69,11 +69,6 @@ public:
         is_multicore = is_multicore_;
     }
 
-    /// Check if it's using host timing.
-    bool IsHostTiming() const {
-        return is_multicore;
-    }
-
     /// Pauses/Unpauses the execution of the timer thread.
     void Pause(bool is_paused);