Removed the MainLatest feed from nuget.config

[Arlodotexe]

Fixes #664

PR Type

This PR fixes an issue where opening or building the solution results in an error "Error occurred while getting package vulnerability data"

What is the current behavior?

What is the new behavior?

PR Checklist

Please check if your PR fulfills the following requirements:

• Created a feature/dev branch in your fork (vs. submitting directly from a commit on main)
• Based off latest main branch of toolkit
• Tested code with current supported SDKs
• New component
  • Documentation has been added
  • Sample in sample app has been added
  • Analyzers are passing for documentation and samples
  • Icon has been created (if new sample) following the Thumbnail Style Guide and templates
• Tests for the changes have been added (if applicable)
• Header has been added to all new source files
• Contains NO breaking changes

Other information

[michael-hawker]

This seems like a remnant anyway, we don't need anything from the MainLatest feed. Ideally we should ensure the Toolkit is self-contained or only uses stable bits in the Toolkit.