environ: Don't expose get_environ_ptr in csdlib

since it isn't defined in c/c++ standard

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

include/cxx/cstdlib

@@ -42,9 +42,6 @@ namespace std
 
   // Environment variable support
 
-#ifndef CONFIG_DISABLE_ENVIRON
-  using ::get_environ_ptr;
-#endif
   using ::getenv;
   using ::putenv;
   using ::clearenv;