Clarify that there's no need for MSA when signing in with GitHub

[captainbrosset]

Rendered article section for review:

• Publish a Microsoft Edge extension by using a GitHub account - bottom of Intro section
  • Internal preview: https://review.learn.microsoft.com/microsoft-edge/extensions-chromium/publish/github?branch=pr-en-us-3058
  • Public preview: https://github.com/MicrosoftDocs/edge-developer/blob/main/microsoft-edge/extensions-chromium/publish/github.md
  • Before/Live: https://learn.microsoft.com/microsoft-edge/extensions-chromium/publish/github

This PR fixes #2716 by removing a confusing sentence about linking your github account to your MSA account. An MSA account is not needed in this scenario, so this sentence is confusing.

AB#48990073

[learn-build-service-prod[bot]]

Learn Build status updates of commit bda1a37:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
microsoft-edge/extensions-chromium/publish/github.md	:white_check_mark:Succeeded	View

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel