Just happened across an application where EquationSystems::delete_system() might be quite useful, so I went to check the docs...

   598    benkirk   /**
   598    benkirk    * Remove the system named \p name from the systems array.
  1812   roystgnr    * This function is now deprecated - write the
  1812   roystgnr    * libmesh-devel mailing list if you need it reimplemented.
   598    benkirk    */
   598    benkirk   void delete_system (const std::string& name);

So here we are 4,000 svn revisions later, the method is still in there and Im dubious that it will work right if it is called.

Roy, do you happen to remember what led up to the deprecation?

I suppose asking the list to reimplement it would be an exercise in futility, but if we can figure out what the issues were I might be able to do something about it...