Delete the "update email" functionality from signup

What does this MR do and why?

Part (1/3) (frontend cleanup) of this issue: #550449 (closed)

• Part (2) - will remove backend
• Part (3) - will clean up db columns

This MR removes the frontend component that allowed users to update their email after failure to sign in.

Before

When the Require email verification when account is locked. application setting is checked and email_reset_offered_at feature flag is enabled, then a "update email" button would appear after 3 wrong password attempts and 1 eventual sucessful password attempt:

After

There is no "update email" button and the other associated frontend code has been cleaned up.

How to set up and validate locally

1. Login as admin and visit the sign in settings
2. Verify Require email verification when account is locked. is checked
3. Enable the offer_email_reset feature flag
4. Find a test user
5. Verify in console the user has email_reset_offered_at set to nil
6. Try to sign in the user with a wrong password 3 times
7. Try to sign in the user with a correct password
8. Verify the Update email button is not shown