wallet: unnecessary coinbase chain position assert

[torkelrogstad]

Description

Removes an unneeded assertion from preselect_utxos. I'm not precisely sure how I triggered this, but I encountered this while syncing a rather large signet wallet containing lots of freshly generated UTXOs.

This assertion is not needed, as unconfirmed coinbase TXs get filtered away in the branch below anyways.

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

Bugfixes:

• This pull request breaks the existing API
• I've added tests to reproduce the issue which are now passing
• I'm linking the issue being fixed by this PR

[evanlinjin]

I'm not precisely sure how I triggered this, but I encountered this while syncing a rather large signet wallet containing lots of freshly generated UTXOs.

The fact that there is an unconfirmed coinbase tx signals that there is a bug.

Would you mind describing the conditions that triggered this?

I.e.

• What chain source you used. bdk_electrum, bdk_esplora, something custom, etc.
• whether you did a full-scan request or a sync request (if electrum/esplora) before trying to create tx.
• Wallet state before the sync.

[torkelrogstad]

This might actually be fixed by this recent PR: #1830