Remove broken targets from "all" and "gn_all", under Windows component builds.

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index ffb9200e2dd4a1bb8c5963bb90083a0dd8296551..38275c42fc8eb0cc66583f5df7ef57de12603e4d 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -759,6 +759,12 @@ group("gn_only") {
       "//ui/views/mus:views_mus_unittests",
     ]
 
+    # crbug.com/676055: media_service_unittests fails to link under Windows
+    # component builds, due to duplicate symbol definitions.
+    if (is_win && is_component_build) {
+      deps -= [ "//media/mojo/services:media_service_unittests" ]
+    }
+
     if (use_ozone && is_chromeos) {
       deps += [ "//services/ui/display:display_service_unittests" ]
     }