Remove nodewords_custom.module

nodewords_custom.module is a shell module that is thought to allow users to create custom meta tags. As the module doesn't contain code, and as it is easy for anybody to create a custom module (and maybe most people already created their custom module to contain code specific for their web sites).

Who already added code to the module can still use it (it would be good to rename the module to avoid incompatibilities with the branch 6.x-3, in the case it is planned to update Nodewords to that branch).

I apologize for any problems this could cause; if I would have thought better when I introduced this module, I would have understood that there was no need to create it.

The module will remain in the branch 6.x-3 because it will allow to create custom meta tags through the user interface.