Remove is_win/OS_WIN checks in shell code

We only develop and test mojo_shell on Android and Linux so checking for
windows or posix is not useful since it's either always false (is_win)
or always true (is_posix).

R=viettrungluu@chromium.org

Review URL: https://codereview.chromium.org/1045893004
diff --git a/shell/command_line_util.cc b/shell/command_line_util.cc
index 0a307f6..3c6de7d 100644
--- a/shell/command_line_util.cc
+++ b/shell/command_line_util.cc
@@ -73,13 +73,7 @@
 void RunCommandLineApps(Context* context) {
   const auto& command_line = *base::CommandLine::ForCurrentProcess();
   for (const auto& arg : command_line.GetArgs()) {
-    std::string arg2;
-#if defined(OS_WIN)
-    arg2 = base::UTF16ToUTF8(arg);
-#else
-    arg2 = arg;
-#endif
-    GURL url = GetAppURLAndSetArgs(arg2, context);
+    GURL url = GetAppURLAndSetArgs(arg, context);
     if (!url.is_valid())
       return;
     context->Run(url);