[UDP] Cannot remove mandatory Sandbox Test Account fields from UDP Settings array

After installing the Universal Distribution Portal (UDP) package, "UDP Settings" will be exposed to the user which will allow them to add "UDP Sandbox Test Accounts." Currently, these pertaining fields are handled as array items, however they cannot be removed once added from the GUI. This is problematic as these fields are also required by validation to be populated, forcing the user to submit faux data or delete the "UDP Settings" asset to continue using their configuration.

Steps to reproduce:
- In Unity 2019.3, create a new project and nstall the Universal Distribution Portal (UDP) package (alternatively download the attached project)
- Menu: Window > Universal Distribution Portal > Settings
-Inspector (UDP Settings) > Register the project with Unity Cloud Services if the UDP Settings Inspector pane indicates it is not already
- Inspector (UDP Settings) > UDP Sandbox Test Accounts > Add new test account
- Observe there is no way to remove this new test account item from the array
- Inspector (UDP Settings) > Push
- Observe the user cannot Push due to validation issues requiring the UDP Sandbox Test Accounts fields to be populated, though they cannot be removed