AP_HAL: remove register_timer_process with extra arg

libraries/AP_HAL/Scheduler.h

@@ -34,11 +34,6 @@ public:
 
     // register a high priority timer task
     virtual void     register_timer_process(AP_HAL::MemberProc) = 0;
-    virtual bool     register_timer_process(AP_HAL::MemberProc proc, uint8_t freq_div)
-    {
-        register_timer_process(proc);
-        return false;
-    }
 
     // register a low priority IO task
     virtual void     register_io_process(AP_HAL::MemberProc) = 0;