Remove mojo::String.

mojo/public/cpp/bindings/tests/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 source_set("tests") {
   testonly = true
 
   sources = [
     "array_common_test.h",
     "array_unittest.cc",
@@ skipping 14 matching lines @@
     "interface_ptr_unittest.cc",
     "message_queue.cc",
     "message_queue.h",
     "multiplex_router_unittest.cc",
     "report_bad_message_unittest.cc",
     "request_response_unittest.cc",
     "router_test_util.cc",
     "router_test_util.h",
     "sample_service_unittest.cc",
     "serialization_warning_unittest.cc",
-    "string_unittest.cc",
     "struct_unittest.cc",
     "sync_method_unittest.cc",
     "type_conversion_unittest.cc",
     "union_unittest.cc",
     "validation_context_unittest.cc",
     "validation_unittest.cc",
     "variant_test_util.h",
   ]
 
   deps = [
@@ skipping 89 matching lines @@
 source_set("mojo_public_bindings_test_utils") {
   sources = [
     "validation_test_input_parser.cc",
     "validation_test_input_parser.h",
   ]
 
   deps = [
     "//mojo/public/c/system",
   ]
 }