[CHE 202] BE CONTROLLER TESTS - deleteUserByEmail

[brok3turtl3]

Description

This PR creates the test file for deleteUserByEmail. While writing tests the target file was also refactored to use our custom error handlers.

Issue

CHE 201

Testing Instructions

N/A

Checklist

All Team Members

• I added a descriptive title to this PR.
• I filled out the Description, Jira Task, and Testing Instructions sections above.
• I added or updated [Jest unit tests]for any changes to components, server-side controllers, etc.
• I ran npm run docker-test in my local environment to check that this PR passes all unit tests.
• I did a quick check to make sure my code changes follow the recommended style guide.

Additional Notes, Images, etc.

N/A