When you say you asked for a refund, did you ask the vendor or eBay?
If the vendor refunded you, there was no transaction, and removing feedback about a non-existant transaction is simple.
If you opened and won a Dispute/Claim, not only do you get a refund but if the vendor was unco-operative, he gets a Defect on his account.
Defects mean the seller may be paying higher fees, may have the number and value of his listings restricted, and/or may have his account closed. He also had to pay return shipping on the card if he demands it back. You can leave appropriate , calm, and factual feedback.
Note that both paths lead to a discount to you.