Fixes https://github.com/flutter/flutter/issues/145158.
In an ideal world, the `--machine` flag would be strictly a global flag which sub-commands can choose to use (or perhaps just to report a `toolExit` that they don't have a `--machine` supported-mode if not. However currently, there is both a global flag, and command-specific flags.
This leads to the confusing scenario where:
```sh
flutter devices --machine
```
... still checks for a Flutter update, printing a banner and breaking the JSON output.
This PR "fixes" that by allowing `--machine` _anywhere_ in the command-line arguments to suppress the check.
/cc @johnmccutchan.
0cc27b993f