Ensure PolicyTest.CertificateTransparencyEnforcementDisabledForUrls actually tests

During a refactor, an accidental disabling of the CT enforcement crept
in, meaning the test no longer tested that the policy overrode any
CT requirements.

BUG=769401
TBR=pastarmovj@chromium.org

Change-Id: I2c060f0027ad838d4447235fe368f0fa2c1cd2ca
Reviewed-on: https://chromium-review.googlesource.com/998547
Commit-Queue: Ryan Sleevi <rsleevi@chromium.org>
Reviewed-by: Doug Turner <dougt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548850}

chrome/browser/policy/policy_browsertest.cc

@@ -3836,8 +3836,6 @@ IN_PROC_BROWSER_TEST_F(PolicyTest,
   UpdateProviderPolicy(policies);
   FlushBlacklistPolicy();
 
-  SetShouldRequireCTForTesting(nullptr);
-
   ui_test_utils::NavigateToURL(browser(),
                                https_server_ok.GetURL("/simple.html"));