linter: (1/2) enable errcheck (#5064)

## Description

partially cleanup in preparation for errcheck

i ignored a bunch of defer errors in tests but with the update to go 1.14 we can use `t.Cleanup(func() { if err := <>; err != nil {..}}` to cover those errors, I will do this in pr number two of enabling errcheck.

ref #5059

scripts/wal2json/main.go

@@ -48,7 +48,7 @@ func main() {
 		}
 		if err == nil {
 			if endMsg, ok := msg.Msg.(cs.EndHeightMessage); ok {
-				_, err = os.Stdout.Write([]byte(fmt.Sprintf("ENDHEIGHT %d\n", endMsg.Height))) // nolint: errcheck, gas
+				_, err = os.Stdout.Write([]byte(fmt.Sprintf("ENDHEIGHT %d\n", endMsg.Height)))
 			}
 		}
 		if err != nil {