DOC: remove the concept of pre-release notes

[ZLLentz]

Description

Remove the pre-release notes system that I had created some years back

Motivation and Context

• The system is easy to forget to do and adds extra review overhead
• The text is redundant with what github can generate automatically and with what we store in the github releases section
• People usually do it wrong anyway- everyone does it wrong sometimes, even me

How Has This Been Tested?

I'll download and double-check the generated sphinx docs

Where Has This Been Documented?

I updated the pre-merge checklist

Pre-merge checklist

• Code works interactively
• Code contains descriptive docstrings, including context and API
• New/changed functions and methods are covered in the test suite where possible
• Test suite passes locally
• Test suite passes on GitHub Actions

[ZLLentz]

After merging in Truman's changes from #1415 I will need to make one more edit here