Dockerfile: remove sudo

[carlocab]

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Homebrew on Linux is designed to be able to run without sudo. We
should leave it out of our Docker containers to make sure we're not
relying on it anywhere.

[Bo98]

This is a good idea for Homebrew/core PRs but it will break things: https://github.com/Homebrew/actions/blob/5fa6b2b81cecc8034b08c5e05285c9d1ec728e9a/setup-homebrew/main.sh#L78, https://github.com/Homebrew/homebrew-core/blob/34b615381d397dd75abe2861db66d1f970a99c9f/.github/workflows/publish-commit-bottles.yml#L337. Plus various third-party use cases we have no control over.

Maybe some magic in Homebrew/actions/pre-build to neuter sudo might be an alternative solution.

[MikeMcQuaid]

👍🏻 from me when it's working as expected.