clean up dial functions

* add a context to all Dial functions
* remove the explicit Dial{*}Context functions

integrationtests/self/deadline_test.go

@@ -30,6 +30,7 @@ var _ = Describe("Stream deadline tests", func() {
 		}()
 
 		conn, err := quic.DialAddr(
+			context.Background(),
 			fmt.Sprintf("localhost:%d", server.Addr().(*net.UDPAddr).Port),
 			getTLSClientConfig(),
 			getQuicConfig(nil),