Fix instantiations in previews_lite_page_redirect_browsertest.cc

This CL adds instantiations for
PreviewsLitePageRedirectServerBrowserTestWithAlwaysHoldback and removes
the empty instantiation for CoinFlipHoldbackExperimentBrowserTest.

This CL fixes the warnings thrown by browser_tests:
[test_launcher.cc(1498)] The following parameterized test case is not instantiated: UninstantiatedParamaterizedTestSuite<PreviewsLitePageRedirectServerBrowserTestWithAlwaysHoldback>
[test_launcher.cc(1498)] The following parameterized test case is not instantiated: UninstantiatedParamaterizedTestSuite<CoinFlipHoldbackExperimentBrowserTest>

Change-Id: I3ac29a9f8971b8445a8d65e37b2eadc15f3efcd8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2054126
Auto-Submit: Alan Cutter <alancutter@chromium.org>
Commit-Queue: Ryan Sturm <ryansturm@chromium.org>
Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#741201}

chrome/browser/previews/previews_lite_page_redirect_browsertest.cc

@@ -1187,6 +1187,12 @@ class PreviewsLitePageRedirectServerBrowserTestWithAlwaysHoldback
   base::test::ScopedFeatureList feature_list_;
 };
 
+// Param is true if DRP holdback should be enabled.
+INSTANTIATE_TEST_SUITE_P(
+    All,
+    PreviewsLitePageRedirectServerBrowserTestWithAlwaysHoldback,
+    ::testing::Bool());
+
 IN_PROC_BROWSER_TEST_P(
     PreviewsLitePageRedirectServerBrowserTestWithAlwaysHoldback,
     DISABLE_ON_WIN_MAC_CHROMEOS(CoinFlipHoldbackTriggering)) {
@@ -2295,12 +2301,6 @@ class CoinFlipHoldbackExperimentBrowserTestWithCoinFlipHoldbackDisabled
   base::test::ScopedFeatureList feature_list_;
 };
 
-// Param is true if DRP holdback should be enabled.
-INSTANTIATE_TEST_SUITE_P(
-    All,
-    CoinFlipHoldbackExperimentBrowserTest,
-    ::testing::Bool());
-
 INSTANTIATE_TEST_SUITE_P(
     All,
     CoinFlipHoldbackExperimentBrowserTestWithRandomNavigationCoinFlip,