x/evm/keeper: save 24B with Go in-condition variable idiom (#828)

* x/evm/keeper: save 24B with Go in-condition variable idiom

The prior code doubly invoked (*ethereum/go-ethereum/core/types.Transaction).To()
which is quite expensive, and firstly copies 20 bytes each time, then
that gets rounded up to the proper size class/pointer alignment so on
64-bit machines 20B -> 24B.

Isolating a benchmark for this code per issue #826 shows this saves
quite a bit of bytes and some nano seconds which all count up towards
the transactions per seconds being processed:

```shell
$ benchstat before.txt after.txt
name        old time/op    new time/op    delta
CopyAddr-8    38.4ns ± 3%    19.3ns ± 3%  -49.66%  (p=0.000 n=10+10)

name        old alloc/op   new alloc/op   delta
CopyAddr-8     48.0B ± 0%     24.0B ± 0%  -50.00%  (p=0.000 n=10+10)

name        old allocs/op  new allocs/op  delta
CopyAddr-8      2.00 ± 0%      1.00 ± 0%  -50.00%  (p=0.000 n=10+10)
```

Fixes #826

* changelog

* lint

* Revert stray changes that were used in testing

* rm log

Co-authored-by: Federico Kunze Küllmer <federico.kunze94@gmail.com>

server/start.go

@@ -41,8 +41,6 @@ import (
 	storetypes "github.com/cosmos/cosmos-sdk/store/types"
 	sdk "github.com/cosmos/cosmos-sdk/types"
 
-	ethlog "github.com/ethereum/go-ethereum/log"
-	"github.com/tharsis/ethermint/log"
 	ethdebug "github.com/tharsis/ethermint/rpc/ethereum/namespaces/debug"
 	"github.com/tharsis/ethermint/server/config"
 	srvflags "github.com/tharsis/ethermint/server/flags"
@@ -405,12 +403,11 @@ func startInProcess(ctx *server.Context, clientCtx client.Context, appCreator ty
 		}
 	}
 
-	ethlog.Root().SetHandler(log.NewHandler(logger))
-
 	var (
 		httpSrv     *http.Server
 		httpSrvDone chan struct{}
 	)
+
 	if config.JSONRPC.Enable {
 		genDoc, err := genDocProvider()
 		if err != nil {