[dev]: replace shfmt dependency

[jsjoeio]

As discussed in #2771 (comment), it seems silly to require Go and one dependency to contribute to code-server.

Alternative Options

• make all dev commands run in our dev container so then the only dependency is Docker.
• use a prettier plugin like prettier-plugin-sh
• something else

The goal of this issue is to replace the use of shfmt in code-server.

[code-asher]

Fixed in #2891.