Requirement owners and requirement contributors of that version can remove contributors from a requirement if the requirement is in Draft status. Click on the requirement to view the details, and on the right side vertical menu click the contributors icon to view the list of contributors. Next to their name will be an which can be clicked to remove them as a contributor. A confirmation window will pop up to finalize the change.
Users will need to have project permissions to view and edit the requirement to perform this action. Depending on the settings of the user's project permissions, they may be able to view all the project requirements or just a subset of them.