fix: update intro permission control message for clarity

[mj-kiwi]

Description

This PR updates the intro permission control message for clarity.

The previous copy implied that permissions could be edited, while in reality they can only be revoked and re-granted. The wording has been updated to accurately reflect the actual behavior and align with the latest Figma designs.

Related issues

Fixes:

Manual testing steps

1. Open the advanced permissions introduction modal.
2. Verify the updated intro message is displayed.

Screenshots/Recordings

Before

After

Pre-merge author checklist

• I've followed MetaMask 7715 Permissions Snaps Contributor Docs and MetaMask 7715 Permissions Snaps Coding Standards.
• I've completed the PR template to the best of my ability
• I’ve included tests if applicable
• I’ve documented my code using JSDoc format if applicable

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

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Note

Low Risk
Low risk copy-only change to an English locale string; no behavior or logic changes.

Overview
Updates the English (en.json) advanced-permissions intro copy to remove the suggestion that permissions can be edited, clarifying that they can only be revoked from advanced permissions.

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