Remove --ci flag from install_ptvsd.py

[lightme16]

For #7698

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• Title summarizes what is changing
• Has a news entry file (remember to thank yourself!)
• Appropriate comments and documentation strings in the code
• Has sufficient logging.
• Has telemetry for enhancements.
• Unit tests & system/integration tests are added/updated
• Test plan is updated as appropriate
• package-lock.json has been regenerated by running npm install (if dependencies have changed)
• The wiki is updated with any design decisions/details.

[msftclas]

All CLA requirements met.

[codecov-io]

Codecov Report

Merging #7814 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #7814   +/-   ##
=======================================
  Coverage   59.16%   59.16%           
=======================================
  Files         498      498           
  Lines       22254    22254           
  Branches     3578     3578           
=======================================
  Hits        13166    13166           
  Misses       8264     8264           
  Partials      824      824

---

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 1536d8b...a58b979. Read the comment docs.

[lightme16]

I can see that one test is failed due to

The agent: Azure Pipelines 21 lost communication with the server. Verify the machine is running and has a healthy network connection. For more information, see: https://go.microsoft.com/fwlink/?linkid=846610

Looks unrelated to this PR, it seems we need to restart the tests