[web] Add accountPasswordInputRef back to ThreadSettingsDeleteTab

Summary:
Bring back accountPasswordInputRef to ThreadSettingsDeleteTab using the React.useRef() hook.

We clear the input and focus() it on exception in deleteThreadAction.

Depends on D3837

Test Plan:

1. Open ThreadSettingsModal
2. Navigate to Delete tab
3. Enter gibberish for password
4. Ensure that things continue to look/work as expected

Reviewers: def-au1t, palys-swm

Reviewed By: palys-swm

Subscribers: ashoat, Adrian, karol-bisztyga, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3838