Remove unused RX boosted gain mode functions and related preprocessor directives across multiple variants

variants/ikoka_stick_nrf/platformio.ini

@@ -12,7 +12,6 @@ build_flags = ${nrf52_base.build_flags}
   -D P_LORA_TX_LED=11
   -D DISPLAY_CLASS=SSD1306Display
   -D DISPLAY_ROTATION=2
-  -D USE_SX1262
   -D RADIO_CLASS=CustomSX1262
   -D WRAPPER_CLASS=CustomSX1262Wrapper
   -D P_LORA_DIO_1=D1