[Cashtab] Hide scrollbar again after antd update

Summary:
Scrollbar should be hidden in Cashtab (though scrolling is not disabled).

I think this was lost with the antd upgrade. Noticed when started testing some extension changes.

Test Plan: npm start and don't see a scrollbar

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D15402