[web] Allow account deletion for SIWE accounts

Summary:
Context: https://linear.app/comm/issue/ENG-2586/do-not-require-password-when-deleting-siwe-account-on-web

Basically D6099, but for web instead of native.

Test Plan:

1. Able to successfully delete SIWE account:

2. "Traditional" account deletion continues to work as expected:

Reviewers: ashoat, tomek, marcin

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D6349