This follows along in the spirit of #7845 but is orthogonal to
removing `CheckTxAsync` (which will come after the previous commit
lands,) so I thought I'd get it out there earlier.
This change has two main effects:
1. Remove most of the Async methods from the abci.Client interface.
Remaining are FlushAsync, CommitTxAsync, and DeliverTxAsync.
2. Rename the synchronous methods to remove the "Sync" suffix.
The rest of the change is updating the implementations, subsets, and mocks of
the interface, along with the call sites that point to them.
* Fix stringly-typed mock stubs.
* Rename helper method.
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.
