Saved Filters (from projects, or from customer) can be removed.
Deleting a filter does not delete any quotes, customers, or other data, only the filter is deleted.
Go to Projects and select Saved Filters from the bottom of the list
The list shows filters by their section (e.g. quotations, invoices) and the filter name.
Highlight the one to remove and click 
Delete, then confirm by clicking Yes.