go.crypto: revert 7f5a59ff6b43.

This change reverts https://golang.org/cl/10113043/ because
some folks are stuck on 1.0 till 1.1.1 comes out.

R=golang-dev
CC=golang-dev
https://golang.org/cl/10151043

ssh/session_test.go

@@ -62,6 +62,7 @@ func dial(handler serverType, t *testing.T) *ClientConn {
 				handler(ch.(*serverChan), t)
 			}()
 		}
+		<-done
 	}()
 
 	config := &ClientConfig{