[Cashtab] Disabled scroll wheel within input fields

Summary: Related to T2744. Removed ability to scroll within amount input fields in SendBch, Burn eToken amount input and Send eToken amount input. I think this is a welcome change and should be implemented.

Test Plan:
cd web/cashtab && npm start
navigate to Send screen
click on the 'Amount' input and scroll
observe that the input loses focus

navigate to send eToken screen
click on the 'Amount' input and scroll
observe that the input loses focus

on the same screen, click on the 'Burn eToken' input and scroll
observe that the input loses focus

Reviewers: bytesofman, #bitcoin_abc, emack

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D12409