Fix <DataTable> does not allow to put a button in the column's header

[slax57]

Problem

<DataTable> does not allow to put a button in the column's header (the pointer events are disabled)

Solution

Remove unnecessary wrapper <TableSortLabel disabled>

How To Test

http://localhost:9010/?path=/story/ra-ui-materialui-list-datatable--header-button

Additional Checks

• The PR targets master for a bugfix or a documentation fix, or next for a feature
• The PR includes unit tests (if not possible, describe why) -> not really relevant to me as this is purely CSS issue
• The PR includes one or several stories (if not possible, describe why)
• The documentation is up to date

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