Remove deprecated `--output` format flags

[dylan-apollo]

❗ Breaking Change!

For about a year, Rover has printed a warning that future versions will fail when running commands with --output [json|plain], and that --format [json|plain] should be used instead.

This warning has been removed alongside the code for backwards compatibility.

Warning: You should update any usage of rover [SUBCOMMAND] --output [json|plain] to rover [SUBCOMMAND] --format [json|plain] as of the next release. Passing --output json will write plain text to ./json.

[dylan-apollo]

@abernix done! And I fixed my GPG signature 😁.

We gotta get this repo set up with changesets!

[abernix]

@dylan-apollo I'll probably have trust you to get this over the line at this point because I'm not tracking it much myself anymore. 😉