Use PlatformIO 4 default dir structure (#14879)

buildroot/bin/env_clean

@@ -3,6 +3,7 @@
 rm -rf .pioenvs
 rm -rf .piolibdeps
 rm -rf .piolib
+rm -rf .pio
 
 if [[ $1 = "--deep" ]]; then
   rm -rf ~/.platformio/packages/*