Discuss: Remove pages from docs

As discussed in the TC, we will move forward with this suggestion, leaving the door open for potentially adding a page in the future for "Sponsors" (when we have them) and for OS frameworks that we closely collaborate with. These additions will be addressed in the future if/when appropriate. We won't keep the content (other than in Git history).

Per these issues

• https://github.com/expressjs/discussions/issues/211
• https://github.com/expressjs/discussions/issues/105

Let's remove these ancillary pages. This will also enable us to close a number of other open issues and PRs.

In the "Resources" menu:

• Template engines * (NOTE: This is in addition to the "Guide > Using template engines" and "Advanced topics > Developing template engines" topics)
• Companies using Express
• Open source projects using Express *
• Additional learning * NOTE: THIS IS LOCALIZED
• Frameworks built on Express *

And these under the "Advanced" menu:

• Process managers * NOTE: THIS IS LOCALIZED
• Health Checks and Graceful Shutdown > Third-party solutions

* These are marked with this warning:

Warning: This information refers to third-party sites, products, or modules that are not maintained by the Expressjs team. Listing here does not constitute an endorsement or recommendation from the Expressjs project team.

How to do it

Remove these files:

en dir:

• resources/template-engines.md
• resources/companies-using-express.md
• resources/open-source-using-express.md
• resources/learning.md
• resources/frameworks.md
• advanced/pm.md
• advanced/healthcheck-graceful-shutdown.md section ## Third-party solutions

6 files total, plus part of one file

All other lang dirs:

• advanced/pm.md
• resources/learning.md

2 * 15 langs = 30 files total

Grand total of 36 files removed.