encoding: remove unused benchV1 flag

Change-Id: Ib86ab31ffa38f85cbb218c114f0e6697e3df61d8
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/221018
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/encoding/bench_test.go b/encoding/bench_test.go
index d181085..490656b 100644
--- a/encoding/bench_test.go
+++ b/encoding/bench_test.go
@@ -5,7 +5,6 @@
 package encoding_test
 
 import (
-	"flag"
 	"fmt"
 	"testing"
 
@@ -20,8 +19,6 @@
 // to real world peformance. They are mainly useful as a quick check to
 // detect unexpected regressions and for profiling specific cases.
 
-var benchV1 = flag.Bool("v1", false, "benchmark the v1 implementation")
-
 const maxRecurseLevel = 3
 
 func makeProto() *tpb.TestAllTypes {