Clean up output directory before copying over new files (#14085)
Clean up output directory before copying over new files (#14085)

* Clean up output directory before copying over new files

* Use standard clean task command

cbracken/flutter,cbracken/flutter,tvolkert/flutter,flutter/flutter,Hixie/flutter,flutter/flutter,Hixie/flutter,Hixie/flutter,cbracken/flutter,cbracken/flutter,tvolkert/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,flutter/flutter,flutter/flutter,cbracken/flutter,tvolkert/flutter,cbracken/flutter,Hixie/flutter,cbracken/flutter,flutter/flutter,Hixie/flutter,Hixie/flutter,tvolkert/flutter,cbracken/flutter,flutter/flutter,tvolkert/flutter,tvolkert/flutter,tvolkert/flutter,Hixie/flutter,flutter/flutter,cbracken/flutter,Hixie/flutter,flutter/flutter,tvolkert/flutter,tvolkert/flutter,Hixie/flutter,tvolkert/flutter,flutter/flutter