Remove requirement that mojo::Environment be instantiated.

mojo/public/cpp/environment/lib/logging_only_environment.cc

 // Copyright 2015 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.
 
 // This is a minimal definition of |Environment| that includes only a logger.
 // This is just enough to be able to use |MOJO_LOG()| and related macros in
 // logging.h.
 
 #include "mojo/public/cpp/environment/environment.h"
 
 #include "mojo/public/cpp/environment/lib/default_logger.h"
 
 namespace mojo {
 
-Environment::Environment() {}
-
-Environment::Environment(const MojoAsyncWaiter* default_async_waiter,
-                         const MojoLogger* default_logger) {}
-
-Environment::~Environment() {}
-
 // static
 const MojoLogger* Environment::GetDefaultLogger() {
   return &internal::kDefaultLogger;
 }
 
 }  // namespace mojo