Remove duplicate application cpp files in mojo/application.

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 9dbfaaebb404cf15d43264672a1253cbe3931df5..73ed7ce864c44eaa9718b71004cc4cbb08ae216b 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -92,7 +92,7 @@ group("both_gn_and_gyp") {
     "//media/cast:cast_unittests",
     "//media/midi:midi_unittests",
     "//mojo",
-    "//mojo/application",
+    "//mojo/application/public/cpp",
     "//mojo/common:mojo_common_unittests",
     "//net:hpack_example_generator",
     "//net:hpack_fuzz_mutator",
@@ -444,7 +444,7 @@ group("both_gn_and_gyp") {
       "//gpu/khronos_glcts_support:khronos_glcts_test",  # TODO(GYP) crbug.com/471903 to make this complete.
       "//media/cast:cast_benchmarks",
       "//media/cast:tap_proxy",
-      "//mojo/application",
+      "//mojo/application/public/cpp",
       "//skia:filter_fuzz_stub",
       "//skia:image_operations_bench",
       "//sync/tools:sync_client",
@@ -696,7 +696,6 @@ group("gn_mojo_targets") {
       "//media/mojo/interfaces:interfaces_python",
       "//media/mojo/services:cdm_service",
       "//media/mojo:tests",
-      "//mojo/application/public/cpp:test_support_standalone",
       "//mojo:tests",
       "//net/interfaces:interfaces_python",
       "//third_party/mojo/src/mojo/edk/js/test:js_integration_tests",