[mojo-sdk] Remove mojo_ignore_result and move C++ macros.h to bindings internal code.

mojo/public/c/system/macros.h

Index: mojo/public/c/system/macros.h
diff --git a/mojo/public/c/system/macros.h b/mojo/public/c/system/macros.h
index ce8417086e1ab7336c3cebf01646b7b829aa74b3..917c69cc1569a183beb4d034e65759b3b83d3cfb 100644
--- a/mojo/public/c/system/macros.h
+++ b/mojo/public/c/system/macros.h
@@ -7,20 +7,6 @@
 
 #include <stddef.h>
 
-#ifdef __cplusplus
-// Used to explicitly mark the return value of a function as unused. If you are
-// really sure you don't want to do anything with the return value of a function
-// that has been marked WARN_UNUSED_RESULT, wrap it with this. Example:
-//
-//   scoped_ptr<MyType> my_var = ...;
-//   if (TakeOwnership(my_var.get()) == SUCCESS)
-//     mojo_ignore_result(my_var.release());
-//
-template <typename T>
-inline void mojo_ignore_result(const T&) {
-}
-#endif
-
 // Assert things at compile time. (|msg| should be a valid identifier name.)
 // This macro is currently C++-only, but we want to use it in the C core.h.
 // Use like: