[Cashtab] Remove color change of address on hover in contact list

Summary: Related to T2470. Removed color change of address 'on hover' in contact list.

Test Plan:
cd web/cashtab && npm start
navigate to configure screen
ensure there is at least one contact in the contact list
hover over the contact address
observe that the background color does not change

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D11831