gh-37054: `CODE_OF_CONDUCT.md`: Do not send people to sage-flame
    
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Facts:
- The only place where sage-flame is mentioned is at the bottom of the
Code of Conduct, moved from the Sage wiki to the repository in Apr 2022
in #33565 (this PR has pointers to the discussions that established the
Code in 2014, including the role of sage-flame)
- Moving discussions to sage-flame is the *only* sanction that is
mentioned in the Code of Conduct.
- The sage-flame list/group has not seen a use after 2019.

Here we remove the mention of sage-flame from the Code of Conduct; not
only because it has fallen out of actual use, but also because it is
harmful:
- It is the only sanction mentioned in CoC, and it paints the picture of
symmetric behavior: two or more participants engage in a "heated
discussion".
- Hence it ignores the asymmetric nature of abuse: There is an abuser,
and there is a target of the abuse.
- Sending both to sage-flame is inappropriate and harmful, as it
effectively downplays and legitimizes the conduct of the abuser.

References:
- https://www.shrm.org/topics-tools/news/managing-smart/damage-done-
dealing-narcissists-workplace
- https://edib.harvard.edu/calling-and-calling-out-guide

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- [ ] The description explains in detail what this PR is about.
- [ ] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation accordingly.

### ⌛ Dependencies

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URL: #37054
Reported by: Matthias Köppe
Reviewer(s): roed314

Author: Release Manager

CODE_OF_CONDUCT.md

@@ -37,6 +37,4 @@ Sage can more effectively collaborate with others if they follow this code.
 
 If you believe someone is violating the code of conduct, we ask that you report
 it to https://groups.google.com/g/sage-abuse. The group administrators will
-consider the issue and explore resolutions. It is also possible to move heated
-discussions to https://groups.google.com/g/sage-flame.
-
+consider the issue and explore resolutions.