pio: remove the note about PIO incompatibility

ref. 6af2bad123
2.3.0 is still not supported, but at least buildable

code/platformio.ini

@@ -34,10 +34,6 @@ extra_configs =
 #   arduino core 2.7.1 = espressif8266@2.5.3 (platform)
 #   arduino core 2.7.4 = espressif8266@2.6.2 (platform_latest)
 #
-# Arduino Core 2.3.0:
-#   "Error: Development platform 'espressif8266' is not compatible with PlatformIO Core v4.4.0-b.1 and depends on PlatformIO Core ^3.0.0"
-#   ref. https://docs.platformio.org/en/latest/core/history.html
-#
 # ------------------------------------------------------------------------------
 
 platform = espressif8266@2.5.3