Remove release_notes from process

[davidmrdavid]

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Issue describing the changes in this PR

From my last conversation with @Francisco-Gamino, I understood that we were dropping the use of release_notes.md from our PR-making process. Assuming I understand that correctly, I made this PR to remove the release_notes.md file from the repo, as well as removing the instruction to use it in our PR-making template.

Pull request checklist

• [x] My changes do not require documentation changes
  • [ ] Otherwise: Documentation issue linked to PR
• [x] My changes should not be added to the release notes for the next release
  • [ ] Otherwise: I've added my notes to release_notes.md
• [ ] My changes do not need to be backported to a previous version
  • [ ] Otherwise: Backport tracked by issue/PR #issue_or_pr
• [x] I have added all required tests (Unit tests, E2E tests)

Additional information

[Francisco-Gamino]

@AnatoliB / @michaelpeng36 -- In our current release process, we manually generate the release notes. Do you have any concerns with this change?

[michaelpeng36]

@Francisco-Gamino @davidmrdavid, I think release_notes.md are primarily useful when it's hard to keep track of the work that was done since the last release. If we have been manually generating release notes for PowerShell worker releases up until this point without any issue, then this change seems like a good way to move forward to me.

[AnatoliB]

I'm ok either way. As far as I understand, unlike some other repos, this repo does not have automation to generate release notes automatically from a file today. I think it would be great to get there eventually, perhaps as a part of automating the worker release pipeline in general. But, since this is not implemented today, we can clean it up for now, just to avoid a confusion.