Revert "ADC: fixed HIL build"

This reverts commit 86c1a6a5fdd929516cf0f64f4d610cfcd4b4f774.

ADC will now be disabled on APM2

libraries/AP_ADC/AP_ADC_HIL.cpp

@@ -49,11 +49,6 @@ float AP_ADC_HIL::Ch(unsigned char ch_num)
 	return adcValue[ch_num];
 }
 
-// enable a channel
-void AP_ADC_HIL::enable_channel(uint8_t ch)
-{
-}
-
 // Read 6 channel values
 uint32_t AP_ADC_HIL::Ch6(const uint8_t *channel_numbers, uint16_t *result)
 {

libraries/AP_ADC/AP_ADC_HIL.h

@@ -37,7 +37,6 @@ class AP_ADC_HIL : public AP_ADC
 	///
 	// Read 6 sensors at once
 	uint32_t Ch6(const uint8_t *channel_numbers, uint16_t *result);
-	void enable_channel(uint8_t ch);
 
 	///
 	// Set the adc raw values given the current rotations rates,