gofix -r mapdelete

R=golang-dev, r, adg, r, cw
CC=golang-dev
https://golang.org/cl/5266045
diff --git a/src/pkg/net/fd.go b/src/pkg/net/fd.go
index e46e120..80d40af 100644
--- a/src/pkg/net/fd.go
+++ b/src/pkg/net/fd.go
@@ -152,7 +152,7 @@
 	if !ok {
 		return nil
 	}
-	s.pending[key] = nil, false
+	delete(s.pending, key)
 	return netfd
 }
 
@@ -195,7 +195,7 @@
 		}
 		if t > 0 {
 			if t <= now {
-				s.pending[key] = nil, false
+				delete(s.pending, key)
 				if mode == 'r' {
 					s.poll.DelFD(fd.sysfd, mode)
 					fd.rdeadline = -1
diff --git a/src/pkg/net/fd_linux.go b/src/pkg/net/fd_linux.go
index 70fc344..c860c84 100644
--- a/src/pkg/net/fd_linux.go
+++ b/src/pkg/net/fd_linux.go
@@ -105,7 +105,7 @@
 		if e := syscall.EpollCtl(p.epfd, syscall.EPOLL_CTL_DEL, fd, nil); e != 0 {
 			print("Epoll delete fd=", fd, ": ", os.Errno(e).String(), "\n")
 		}
-		p.events[fd] = 0, false
+		delete(p.events, fd)
 	}
 }
 
diff --git a/src/pkg/net/textproto/header.go b/src/pkg/net/textproto/header.go
index 288deb2..7fb32f8 100644
--- a/src/pkg/net/textproto/header.go
+++ b/src/pkg/net/textproto/header.go
@@ -39,5 +39,5 @@
 
 // Del deletes the values associated with key.
 func (h MIMEHeader) Del(key string) {
-	h[CanonicalMIMEHeaderKey(key)] = nil, false
+	delete(h, CanonicalMIMEHeaderKey(key))
 }
diff --git a/src/pkg/net/textproto/pipeline.go b/src/pkg/net/textproto/pipeline.go
index 8c25884..ca50edd 100644
--- a/src/pkg/net/textproto/pipeline.go
+++ b/src/pkg/net/textproto/pipeline.go
@@ -108,7 +108,7 @@
 	}
 	c, ok := s.wait[id]
 	if ok {
-		s.wait[id] = nil, false
+		delete(s.wait, id)
 	}
 	s.mu.Unlock()
 	if ok {