SRV_Channels: gate method on scripting being enabled

also AP_Scheduler since we're calling and instance method on it

libraries/SRV_Channel/SRV_Channels.cpp

@@ -474,6 +474,7 @@ void SRV_Channels::set_output_pwm_chan(uint8_t chan, uint16_t value)
     }
 }
 
+#if AP_SCRIPTING_ENABLED && AP_SCHEDULER_ENABLED
 // set output value for a specific function channel as a pwm value with loop based timeout
 // timeout_ms of zero will clear override of the channel
 // minimum override is 1 MAIN_LOOP
@@ -499,6 +500,7 @@ void SRV_Channels::set_output_pwm_chan_timeout(uint8_t chan, uint16_t value, uin
         }
     }
 }
+#endif  // AP_SCRIPTING_ENABLED
 
 /*
   wrapper around hal.rcout->cork()