Remove pick into x.y message from Danger

What does this MR do and why?

Remove pick into x.y message from Danger

At the moment, merge requests prepared in canonical are either:

• Preparation branches created by release managers
• Backport requests approved.

In both cases, the Pick into x.x is not necessary. This commit removes an unuseful message from Danger.

Related to gitlab-com/gl-infra/delivery#2839 (closed)

MR acceptance checklist

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