Remove unused entityLog struct

Since the logging refactoring in 27e090, entityLog is not used anymore
and can be removed.

upstream.go

@@ -7,7 +7,6 @@ import (
 	"fmt"
 	"io"
 	"net"
-	"os"
 	"strconv"
 	"strings"
 	"time"
@@ -64,11 +63,6 @@ type upstreamConn struct {
 	messageLoggers map[string]*messageLogger
 }
 
-type entityLog struct {
-	name string
-	file *os.File
-}
-
 func connectToUpstream(network *network) (*upstreamConn, error) {
 	logger := &prefixLogger{network.user.srv.Logger, fmt.Sprintf("upstream %q: ", network.Addr)}