remove the no longer needed ignore: cancel_subscriptions (#7542)
remove the no longer needed ignore: cancel_subscriptions (#7542)

This has been fixed: https://github.com/dart-lang/linter/issues/317
cbracken/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,flutter/flutter,tvolkert/flutter,flutter/flutter,flutter/flutter,Hixie/flutter,tvolkert/flutter,tvolkert/flutter,tvolkert/flutter,cbracken/flutter,turnidge/flutter,tvolkert/flutter,turnidge/flutter,Hixie/flutter,Hixie/flutter,turnidge/flutter,turnidge/flutter,flutter/flutter,Hixie/flutter,tvolkert/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,tvolkert/flutter,tvolkert/flutter,tvolkert/flutter,cbracken/flutter,cbracken/flutter,Hixie/flutter,flutter/flutter,cbracken/flutter,flutter/flutter,flutter/flutter,cbracken/flutter,tvolkert/flutter,Hixie/flutter,cbracken/flutter,flutter/flutter,Hixie/flutter,Hixie/flutter,cbracken/flutter,turnidge/flutter