To support non-interactive (address) full value sends, tombstone outputs are sometimes created.
They do contain an asset commitment to prove the previous asset split, but have a value of 0 on the asset level.
Currently those tombstone outputs are put into a BTC anchor output of 1k sats but then aren't ever used by the wallet anymore.

We should garbage collect those tombstone outputs when creating new on-chain transactions (e.g. when sending other assets).
The following list should roughly describe the steps necessary:

• Create a method to query for managed anchor UTXOs that have 0 effective value (counting burns as 0 value) on the asset level
• When creating a new on-chain transaction, add all currently available tombstone anchor UTXOs as inputs

Because we don't currently clean up those empty outputs, we explicitly don't allow burning all assets within an anchor output. But with this cleanup mechanism in place, we might decide to allow that now.