[web] Push accountPassword state and related functionality down to ThreadSettingsDeleteTab

Summary:
We don't need to be holding onto this state in the parent component and passing it down to ThreadSettingsDeleteTab as a prop.

Depends on D3838

Test Plan: Careful reading, just drag and drop

Reviewers: def-au1t, palys-swm

Reviewed By: palys-swm

Subscribers: ashoat, Adrian, karol-bisztyga, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3840