Remove an obsolete TODO in DataTable

[dkwingsmt]

When the InkWell was added, it was used only for a gesture callback, and at that time the InkWell should only be added when the gesture callback was needed. Due to an issue, we couldn't swap out the child widget dynamically.

Even though that the issue has been fixed, the InkWell is considered mandatory since it is now used by two more properties. (Theoretically we can check if any of the 3 properties is needed to add this InkWell, but I think that's too much.)

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[gemini-code-assist]

Code Review

This pull request removes an obsolete TODO comment from the DataTable widget. The TODO suggested conditionally wrapping a header cell label in an InkWell, but as the PR description explains, the InkWell is now always necessary for handling properties like overlayColor and mouseCursor, making the conditional wrapping logic unnecessary. The change is a straightforward code cleanup.

[chunhtai]

LGTM