Was: tendermint/tendermint#9388

In light of ABCI++ landing and, as per the previous discussion in tendermint/tendermint#9388, it was decided to first deprecate the priority mempool for v0.37 and then remove it from v0.38, as its functionality can be obtained by implementing an app-side mempool with ABCI++.

ToDo

For v0.37.1:

• Mark priority mempool as deprecated in v0.37.x #259

For v0.38.0:

• Remove priority mempool from v0.38 #260