fix: missing validation for backend option in remove command

[matthisholleville]

Closes #

📑 Description

The commit fixes an issue where the --backend option was not properly validated in the remove command.

Previously, the command did not check if the --backend option was set, leading to potential errors. This fix ensures that the option is required and throws an error if it is missing.

✅ Checks

• My pull request adheres to the code style of this project
• My code requires changes to the documentation
• I have updated the documentation as required
• All the tests have passed

ℹ Additional Information