[web] Delete all the unnecessary code from delete account modal

Summary:
This diff deletes all the code and styles that are not a part of the final modal. The next diff will update the styling.

Depends on D4117

Test Plan: Show the modal and check if only heading, message, password input and delete button are shown.

Reviewers: def-au1t, atul, benschac

Reviewed By: atul

Subscribers: ashoat, Adrian, yayabosh

Differential Revision: https://phabricator.ashoat.com/D4118