all: remove dependency on proto v1

This does not remove all dependencies,
but all of the cases where it can now be implemented in terms of v2.

Change-Id: Idc5b0273f0d35c284bf2141eb9cce998692ceb15
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/184878
Reviewed-by: Herbie Ong <herbie@google.com>
diff --git a/encoding/prototext/decode_test.go b/encoding/prototext/decode_test.go
index 7f0a4e8..799de2e 100644
--- a/encoding/prototext/decode_test.go
+++ b/encoding/prototext/decode_test.go
@@ -8,7 +8,6 @@
 	"math"
 	"testing"
 
-	protoV1 "github.com/golang/protobuf/proto"
 	"google.golang.org/protobuf/encoding/prototext"
 	pimpl "google.golang.org/protobuf/internal/impl"
 	"google.golang.org/protobuf/internal/scalar"
@@ -1498,7 +1497,7 @@
 			if err == nil && tt.wantErr {
 				t.Error("Unmarshal() got nil error, want error\n\n")
 			}
-			if tt.wantMessage != nil && !protoV1.Equal(tt.inputMessage.(protoV1.Message), tt.wantMessage.(protoV1.Message)) {
+			if tt.wantMessage != nil && !proto.Equal(tt.inputMessage, tt.wantMessage) {
 				t.Errorf("Unmarshal()\n<got>\n%v\n<want>\n%v\n", tt.inputMessage, tt.wantMessage)
 			}
 		})