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

variants/meshtiny/platformio.ini

@@ -6,7 +6,6 @@ build_flags = ${nrf52_base.build_flags}
   -I lib/nrf52/s140_nrf52_6.1.1_API/include
   -I lib/nrf52/s140_nrf52_6.1.1_API/include/nrf52
   -I variants/meshtiny
-  -D USE_SX1262
   -D RADIO_CLASS=CustomSX1262
   -D WRAPPER_CLASS=CustomSX1262Wrapper
   -D LORA_TX_POWER=22