vp9 resize_test: Enable resize_allowed in real-time ExternalResize test.

For dynamic resizing (whether the new codec size is determined internally
or externally set by user), we should for now keep rc.resize_allowed enabled.
This prevent the use of referene_masking for real-time mode
(in set_rt_speed_feature()).

Change-Id: Ibb7c3ff35be88afdf1a3c6db6693521766f177a3

test/resize_test.cc

diff --git a/test/resize_test.cc b/test/resize_test.cc
index c5f05f3..10f7fe2 100644
--- a/test/resize_test.cc
+++ b/test/resize_test.cc
@@ -387,8 +387,6 @@
 TEST_P(ResizeRealtimeTest, TestExternalResizeWorks) {
   ResizingVideoSource video;
   DefaultConfig();
-  // Disable internal resize for this test.
-  cfg_.rc_resize_allowed = 0;
   change_bitrate_ = false;
   ASSERT_NO_FATAL_FAILURE(RunLoop(&video));