refactor(util): remove unused isObject function

[jsjoeio]

Jest reported uncovered code for this function block. I did a search and couldn't find it used anywhere so decided we should remove it.

Related to #5149 #5153

[github-actions]

✨ code-server docs for PR #5183 is ready! It will be updated on every commit.

• Host: https://coder.com/docs/code-server/b29af6c
• Last deploy status: success
• Commit: 61a7ffd
• Workflow status: https://github.com/coder/code-server/actions/runs/2297490550

[codecov]

Codecov Report

Merging #5183 (b29af6c) into main (3207bfd) will increase coverage by 0.02%.
The diff coverage is n/a.

❗ Current head b29af6c differs from pull request most recent head 61a7ffd. Consider uploading reports for the commit 61a7ffd to get more accurate results

@@            Coverage Diff             @@
##             main    #5183      +/-   ##
==========================================
+ Coverage   71.79%   71.81%   +0.02%     
==========================================
  Files          30       30              
  Lines        1691     1689       -2     
  Branches      375      374       -1     
==========================================
- Hits         1214     1213       -1     
  Misses        408      408              
+ Partials       69       68       -1     

Impacted Files	Coverage Δ
src/node/util.ts	82.58% <ø> (+0.36%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 3207bfd...61a7ffd. Read the comment docs.

[github-actions]

✨ code-server dev build published to npm for PR #5183!

• Last publish status: success
• Commit: 61a7ffd

To install in a local project, run:

npm install @coder/code-server-pr@5183

To install globally, run:

npm install -g @coder/code-server-pr@5183