refactor: remove dead code

[jsjoeio]

This PR removes dead (unused) code. It also moves a function only used in tests to the test helpers section of the codebase.

Changes

• refactor: delete unused code
• refactor: move onLine to test helpers

How this was done

1. npx ts-prune --project tsconfig.json | grep -v '(used in modules)' | grep -v 'typings'
2. removed code based on functions listed

Related to #5149

[github-actions]

✨ code-server docs for PR #5188 is ready! It will be updated on every commit.

• Host: https://coder.com/docs/code-server/c7ecd64
• Last deploy status: success
• Commit: 9aad95b
• Workflow status: https://github.com/coder/code-server/actions/runs/2303670917

[codecov]

Codecov Report

Merging #5188 (9aad95b) into main (1788537) will decrease coverage by 0.23%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #5188      +/-   ##
==========================================
- Coverage   71.81%   71.58%   -0.24%     
==========================================
  Files          30       30              
  Lines        1689     1668      -21     
  Branches      374      367       -7     
==========================================
- Hits         1213     1194      -19     
+ Misses        408      407       -1     
+ Partials       68       67       -1     

Impacted Files	Coverage Δ
src/common/util.ts	100.00% <ø> (ø)
src/node/app.ts	100.00% <ø> (ø)
src/node/constants.ts	100.00% <ø> (ø)
src/node/util.ts	83.42% <ø> (+0.84%)	⬆️

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[github-actions]

✨ code-server dev build published to npm for PR #5188!

• Last publish status: success
• Commit: 9aad95b

To install in a local project, run:

npm install @coder/code-server-pr@5188

To install globally, run:

npm install -g @coder/code-server-pr@5188