Update custom_modules_in_cpp.rst

remove outdated note referencing a file which no longer exists

contributing/development/core_and_modules/custom_modules_in_cpp.rst

@@ -223,10 +223,6 @@ You can then zip it and share the module with everyone else. When
 building for every platform (instructions in the previous sections),
 your module will be included.
 
-.. note:: There is a parameter limit of 5 in C++ modules for things such
-          as subclasses. This can be raised to 13 by including the header
-          file ``core/method_bind_ext.gen.inc``.
-
 Using the module
 ----------------