Remove TODO comment

Remove the TODO comment for HTML Imports, which are being deprecated
and will be removed.

Change-Id: I36f80d0e90adc06d53c05e3bcb24bd5f766b610e
Reviewed-on: https://chromium-review.googlesource.com/1248382Reviewed-by: Kent Tamura <tkent@chromium.org>
Commit-Queue: Hayato Ito <hayato@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594615}

third_party/blink/renderer/core/html/custom/custom_element_upgrade_sorter_test.cc

@@ -196,6 +196,4 @@ TEST_F(CustomElementUpgradeSorterTest, sorter_shadow) {
   EXPECT_EQ(d, elements[2].Get());
 }
 
-// TODO(kochi): Add test cases which uses HTML imports.
-
 }  // namespace blink