for #4154 use internal pull-ups to power ADC_Ctrl

* Currently only on heltec tracker, but could use ADC_USE_PULLUP on other boards that could benefit
* Thanks @todd-herbert and @StevenCellist for the instructions ;-)
* Remove nasty Heltec_wireless #ifdefs that got somehow added to Power.cpp, instead use proper variant defs
* Cleanup adc enable/disable code a bit for less copy-paste cruft

variants/heltec_wireless_paper_v1/variant.h

@@ -29,6 +29,7 @@
 #define BAT_MEASURE_ADC_UNIT 2          // Use ADC2
 #define ADC_ATTENUATION ADC_ATTEN_DB_12 // Voltage divider output is quite high
 #define HAS_32768HZ
+#define ADC_CTRL_ENABLED LOW
 
 // LoRa
 #define USE_SX1262
@@ -49,4 +50,4 @@
 #define SX126X_RESET LORA_RESET
 
 #define SX126X_DIO2_AS_RF_SWITCH
-#define SX126X_DIO3_TCXO_VOLTAGE 1.8
+#define SX126X_DIO3_TCXO_VOLTAGE 1.8