UPGRADING: polish upgrading instructions for 0.34 (#5398)
UPGRADING: polish upgrading instructions for 0.34 (#5398)

This change adds some polish to the upgrading instructions for 0.34. The only substantive changes include:
* Calling out ABCI-impacting changes explicitly in the "ABCI Changes" section, even if those changes are also mentioned elsewhere
* Removes `ProofOfTrialPeriod` from consensus params; this change was introduced and then removed. 
tendermint/tendermint,tendermint/tendermint,tendermint/tendermint,tendermint/tendermint