Default button polarity to active-LOW across all firmware types

Nearly all LoRa boards use a boot button that pulls to ground when
pressed.

variants/t1000-e/T1000eBoard.h

@@ -78,14 +78,14 @@ public:
     digitalWrite(LED_PIN, HIGH);
     #endif
     #ifdef BUTTON_PIN
-    while(digitalRead(BUTTON_PIN));
+    while(digitalRead(BUTTON_PIN) == LOW);
     #endif
     #ifdef LED_PIN
     digitalWrite(LED_PIN, LOW);
     #endif
 
     #ifdef BUTTON_PIN
-    nrf_gpio_cfg_sense_input(BUTTON_PIN, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_SENSE_HIGH);
+    nrf_gpio_cfg_sense_input(BUTTON_PIN, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_SENSE_LOW);
     #endif
 
     sd_power_system_off();

variants/t1000-e/platformio.ini

@@ -10,7 +10,6 @@ build_flags = ${nrf52_base.build_flags}
   -I src/helpers/ui
   -D T1000_E
   -D PIN_USER_BTN=6
-  -D USER_BTN_PRESSED=HIGH
   -D PIN_STATUS_LED=24
   -D RADIO_CLASS=CustomLR1110
   -D WRAPPER_CLASS=CustomLR1110Wrapper