Move gn _run target generation into test().

ui/display/BUILD.gn

Index: ui/display/BUILD.gn
diff --git a/ui/display/BUILD.gn b/ui/display/BUILD.gn
index 6c6c181ae1ef4dc8d4d28e37195ca655423fc491..b8c760318babbea63d534cd95c37700e53f5f42e 100644
--- a/ui/display/BUILD.gn
+++ b/ui/display/BUILD.gn
@@ -130,15 +130,6 @@ if (is_chromeos) {
   }
 }
 
-# TODO(GYP): Delete this after we've converted everything to GN.
-# The _run targets exist only for compatibility w/ GYP.
-group("display_unittests_run") {
-  testonly = true
-  deps = [
-    ":display_unittests",
-  ]
-}
-
 # This test covers the ChromeOS "display" target as well as the cross-platform
 # //display/util target.
 test("display_unittests") {