Can't Remove Email for Email Routing

### Environment

SaaS (https://sentry.io/)

### Steps to Reproduce

1. Navigate to Account > Notifications > Email Routing
2. Choose an email for a specific project

### Expected Result

Ability to remove an email once it's set.

### Actual Result

Nothing in the UI to remove email after it's set for a particular project.

### Product Area

Settings - Projects

### Link

_No response_

### DSN

_No response_

### Version

_No response_

Start in Account > Notifications > Email Routing and reproduce the missing removal control for a project-specific email. Trace the settings UI and its relevant behavior, then verify that a configured email can be removed and the setting is cleared.

Written by the indexing model from the issue text.