When we do work item customization, we tend to add and remove new fields. Over a time, few fields which we added as part of initial work may not be used. But the unused fields will still appear in your Query editor field list.
Following Witadmin commands will help you to identify the unused fields and clear the same
Command to list all the unused fields
witadmin listfields /collection:http://tfsserver:8080/tfs/DefaultCollection /unused
Commands to delete the specified field say My.SumField
witadmin deletefield /collection:http://tfsserver:8080/tfs/DefaultCollection /n:My.SumField
If you want to double check, whether a field is used or not, use the following command
witadmin listfields /collection:http://tfsserver:8080/tfs/DefaultCollection /n:My.SumField
If it returns “Not In Use“, indicate the field is not used in the project collection
Field: My.SumField
Name: SumField
Type: Integer
Use: Not In Use
Indexed: False
Reportable As: None
Ambilykk's Blog 
Hi Ambily
I’m very impressed by your profile and your experience in .Net technologies. I’m currently using the TFS2013 for agile practices for my team. I customized the process template for the product backlog item and added a new state called Ready. Currently when I marked any PBI as ready, that item is filtered out. I understand the PBI list is filtered in the backlog items, How can i tweak it to see the “Ready” state backlog items. Can you please share the solution?
Is there any email id to reach you?
Hi Neelima
Post more information about the issue, I will respond to you.
Regards
Ambily