Remove static BLE_PIN_CODE definition from Heltec E290_usb configuration

variants/heltec_e290/platformio.ini

@@ -66,7 +66,6 @@ build_flags =
   -D MAX_GROUP_CHANNELS=40
   -D DISPLAY_CLASS=E290Display
   -D AUTO_OFF_MILLIS=0
-  #-D BLE_PIN_CODE=123456   ; dynamic, random PIN
   -D BLE_DEBUG_LOGGING=1
   -D OFFLINE_QUEUE_SIZE=256
 build_src_filter = ${Heltec_E290_base.build_src_filter}