*: move from io/ioutil to io and os packages

The io/ioutil package has been deprecated as of Go 1.16, see
https://golang.org/doc/go1.16#ioutil. This commit replaces the existing
io/ioutil functions with their new definitions in io and os packages.

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

server/embed/serve.go

@@ -17,7 +17,7 @@ package embed
 import (
 	"context"
 	"fmt"
-	"io/ioutil"
+	"io"
 	defaultLog "log"
 	"math"
 	"net"
@@ -92,7 +92,7 @@ func (sctx *serveCtx) serve(
 	handler http.Handler,
 	errHandler func(error),
 	gopts ...grpc.ServerOption) (err error) {
-	logger := defaultLog.New(ioutil.Discard, "etcdhttp", 0)
+	logger := defaultLog.New(io.Discard, "etcdhttp", 0)
 	<-s.ReadyNotify()
 
 	sctx.lg.Info("ready to serve client requests")