devtools

20f3dc67 - Always use tool/flutter-sdk for devtools_tool + remote FLUTTER_ROOT (#6776)

Always use tool/flutter-sdk for devtools_tool + remote FLUTTER_ROOT (#6776) This removes some code I added to support using `FLUTTER_ROOT` for the SDK and instead just updates the `devtools_tool` shell scripts to always run from `tools/flutter-sdk` and just locate the Flutter SDK from the running VM. This makes the assumption that we _always_ want to use the DevTools version of Flutter and avoids any issues where you might have something different on `PATH`. It also renames the `--use-flutter-from-path` flag to `--update-flutter`/`--no-update-flutter` (and retains the default of updating).