[Cashtab] Fix DOM warnings in browser console for message signing properties

Summary:
Corrected TextArea property for Address and Signature

Test Plan:

• npm start
• Display browser dev console
• Navigate to Send page and uncollapse the Sign Message section and ensure the above warning is no longer present
• Ensure Sign message function has not regressed
• Cross check in firefox

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D10489