chore(mergify): revert mergify to stop automatically adding needs-triage label

[maxcao13]

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Fixes: #696

Description of the change:

This change reverts mergify from adding the needs triage label to pull requests.

Motivation for the change:

Mergify kept adding the label, which failed the CI, but removing the label would cause Mergify to add it back.

How to manually test:

1. Start a pull request as a non-cryostat-reviewer.
2. Notice that mergify doesn't add the label anymore.

[maxcao13]

Unfortunately, PRs actually don't get automatically added with the needs-triage label when being made. GitHub hasn't implemented this within the PR template feature yet for some reason. That was why I tried mergify. There is maybe a way to resolve this if I add

• review-requested : reviewers
  as a condition so that the label won't be added when we request from all reviewers, and also make the action a toggle.

There is also just a github action which can do it easier. https://github.com/actions/labeler Thoughts?

[andrewazores]

I think using that Action makes sense. That's a good way to have the label applied only once when a PR is first opened.

[maxcao13]

I'll put it in this pr then.