Update default MR description

What does this MR do and why?

Describe in detail what your merge request does and why.

Update default MR description

Now that we have the %{first_multiline_commit} in the default MR description, the -_Describe in detail what your merge request does and why._ line its redundant with the section title.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.