Use QuicheTest and quiche_test.h in third_party/http2.

The motivation is that these files have to be included with
#pragma clang diagnostic ignored "-Weverything", otherwise CLs touching test
files will not build.

PiperOrigin-RevId: 334632337
Change-Id: I74d8cdef4b07eed79880d1ca7e0476b3a2c5c184
diff --git a/http2/platform/api/http2_test_helpers.h b/http2/platform/api/http2_test_helpers.h
index 4a616f7..53d2d15 100644
--- a/http2/platform/api/http2_test_helpers.h
+++ b/http2/platform/api/http2_test_helpers.h
@@ -5,11 +5,7 @@
 // an AssertionResult if the condition is not satisfied.
 #include "net/http2/platform/impl/http2_test_helpers_impl.h"
 
-#pragma clang diagnostic push
-#pragma clang diagnostic ignored "-Weverything"
-
-#include "testing/gmock/include/gmock/gmock.h"
-#include "testing/gtest/include/gtest/gtest.h"  // For AssertionSuccess
+#include "net/third_party/quiche/src/common/platform/api/quiche_test.h"
 
 #pragma clang diagnostic pop