how to remove TFS workspace mapping for another user

You need to get your TFS administrator to delete the workspace if you have no access to the account.

You may be able to do it by calling “tf workspace” with the explicit user specified, but you need “manage other users workspace” permission. TF Sidekicks uses the same commands so would require the same permission. It is a TFS admin productivity tool.

https://msdn.microsoft.com/en-us/library/y901w7se(v=vs.100).aspx

You can use:

tf workspace /delete "WORKSPACENAME;PREVIOUSUSERACCOUNT"