Clean up migration guide to remove some marketing verbiage

[roaslin]

For a more extended description:

mattermost#6816

[cwarnermm]

@roaslin - This docs PR isn't currently created as a fork against the mattermost/docs GitHub repository; it appears to be linked only to your GitHub account. As a result, we can't apply reviewers and labels and trigger our review pipelines accordingly.

Are you open to creating a new PR against the mattermost/docs repository?

[roaslin]

@roaslin - This docs PR isn't currently created as a fork against the mattermost/docs GitHub repository; it appears to be linked only to your GitHub account. As a result, we can't apply reviewers and labels and trigger our review pipelines accordingly.

Are you open to creating a new PR against the mattermost/docs repository?

🤔 Yes, I followed the steps to create a forkl that is linked to my