remove unused asset.yml
remove unused asset.yml

Forgotten in commit fa05d55191e8e85356872b61f5bbe481738ecb0a

bitcoin-core/bitcoincore.org,bitcoin-core/bitcoincore.org,bitcoin-core/bitcoincore.org,bitcoin-core/bitcoincore.org,bitcoin-core/bitcoincore.org,bitcoin-core/bitcoincore.org