Bug-1943050 userScripts API permissions content (#2013)

* Bug-1943050 userScripts API permissions content

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Co-authored-by: Simeon Vincent <[email protected]>

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- correct the permissions message for `userScripts`
- remove reference to `trialML`

Co-authored-by: Rob Wu <[email protected]>

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Co-authored-by: Simeon Vincent <[email protected]>
Co-authored-by: Rob Wu <[email protected]>

Author: 3 people