net/http/httptrace: remove the mention of http client

This sentence is partially guilty why httptrace is considered as an
http.Client tracing package. Removing the mention.

Updates #17152.

Change-Id: I69f78a6e10817db933f44e464a949ae896e44ec6
Reviewed-on: https://go-review.googlesource.com/29755Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/http/httptrace/trace.go

@@ -65,8 +65,8 @@ func WithClientTrace(ctx context.Context, trace *ClientTrace) context.Context {
 	return ctx
 }
 
-// ClientTrace is a set of hooks to run at various stages of an HTTP
-// client request. Any particular hook may be nil. Functions may be
+// ClientTrace is a set of hooks to run at various stages of an outgoing
+// HTTP request. Any particular hook may be nil. Functions may be
 // called concurrently from different goroutines, starting after the
 // call to Transport.RoundTrip and ending either when RoundTrip
 // returns an error, or when the Response.Body is closed.