gofix -r mapdelete

R=golang-dev, r, adg, r, cw
CC=golang-dev
https://golang.org/cl/5266045
diff --git a/src/pkg/http/persist.go b/src/pkg/http/persist.go
index 78bf905..f73e6c6 100644
--- a/src/pkg/http/persist.go
+++ b/src/pkg/http/persist.go
@@ -165,7 +165,7 @@
 	// Retrieve the pipeline ID of this request/response pair
 	sc.lk.Lock()
 	id, ok := sc.pipereq[req]
-	sc.pipereq[req] = 0, false
+	delete(sc.pipereq, req)
 	if !ok {
 		sc.lk.Unlock()
 		return ErrPipeline
@@ -353,7 +353,7 @@
 	// Retrieve the pipeline ID of this request/response pair
 	cc.lk.Lock()
 	id, ok := cc.pipereq[req]
-	cc.pipereq[req] = 0, false
+	delete(cc.pipereq, req)
 	if !ok {
 		cc.lk.Unlock()
 		return nil, ErrPipeline