all: use time.Until where applicable

Updates #14595

Change-Id: Idf60b3004c7a0ebb59dd48389ab62c854069e09f
Reviewed-on: https://go-review.googlesource.com/28073
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

tls.go

@@ -102,7 +102,7 @@ func DialWithDialer(dialer *net.Dialer, network, addr string, config *Config) (*
 	timeout := dialer.Timeout
 
 	if !dialer.Deadline.IsZero() {
-		deadlineTimeout := dialer.Deadline.Sub(time.Now())
+		deadlineTimeout := time.Until(dialer.Deadline)
 		if timeout == 0 || deadlineTimeout < timeout {
 			timeout = deadlineTimeout
 		}