PR description:
> Originally a follow-up to #19364, this simplifies the logic in ProcessOrphanTx() and removes unused variables.
This is a backport of [[https://github.com/bitcoin/bitcoin/pull/19498 | core#19498]] [1/5]
https://github.com/bitcoin/bitcoin/pull/19498/commits/6e8dd99ef1c147898bd06fee7014afdff6618f18
Note: The `removed_txn` parameter does not exist in ProcessOrphanTx in Bitcoin ABC. This part of the logic was dropped in D1175, and was already unused by then. It seems to be related to RBF (see following comment: https://github.com/bitcoin/bitcoin/pull/21062/commits/f82baf0762f60c2ca5ffc339b095f9271d7c2f33#diff-d3c243938494b10666b44404a27af7d84b44a72b85a27431e0c89e181462ca6eR200)