This is a manual forward-port of #8944 and related fixes from v0.35.x.
One difference of note is that the CheckTx response messages no longer have a
field to record an error from the ABCI application. The code is set up so that
these could be reported directly to the CheckTx caller, but it would be an API
change, and right now a bunch of test plumbing depends on the existing semantics.
Also fix up tests relying on implementation-specific mempool behavior.
- Commit was setting the expected mempool size incorrectly.
- Fix sequence test not to depend on the incorrect size.
Addresses one of the concerns with #7041.
Provides a mechanism (via the RPC interface) to delete a single transaction, described by its hash, from the mempool. The method returns an error if the transaction cannot be found. Once the transaction is removed it remains in the cache and cannot be resubmitted until the cache is cleared or it expires from the cache.
