dep: remove IAVL dependency (#6550)

## Description

remove IAVL as a Tendermint dependency.

closes #5694 

I dont think this needs a changelog entry.

go.mod

@@ -10,11 +10,8 @@ require (
 	github.com/adlio/schema v1.1.13
 	github.com/btcsuite/btcd v0.21.0-beta
 	github.com/btcsuite/btcutil v1.0.2
-	github.com/confio/ics23/go v0.6.6
-	github.com/cosmos/iavl v0.16.0
 	github.com/fortytw2/leaktest v1.3.0
 	github.com/go-kit/kit v0.10.0
-	github.com/go-logfmt/logfmt v0.5.0
 	github.com/gogo/protobuf v1.3.2
 	github.com/golang/protobuf v1.5.2
 	github.com/google/orderedcode v0.0.1
@@ -26,6 +23,7 @@ require (
 	github.com/lib/pq v1.10.2
 	github.com/libp2p/go-buffer-pool v0.0.2
 	github.com/minio/highwayhash v1.0.2
+	github.com/niemeyer/pretty v0.0.0-20200227124842-a10e7caefd8e // indirect
 	github.com/ory/dockertest v3.3.5+incompatible
 	github.com/pkg/errors v0.9.1
 	github.com/prometheus/client_golang v1.10.0
@@ -40,5 +38,7 @@ require (
 	github.com/tendermint/tm-db v0.6.4
 	golang.org/x/crypto v0.0.0-20201117144127-c1f2f97bffc9
 	golang.org/x/net v0.0.0-20201021035429-f5854403a974
+	google.golang.org/genproto v0.0.0-20201119123407-9b1e624d6bc4 // indirect
 	google.golang.org/grpc v1.38.0
+	gopkg.in/check.v1 v1.0.0-20200902074654-038fdea0a05b // indirect
 )