OptimalControl.jl private functions

clean(d::Tuple{Vararg{Symbol}}) -> Tuple{Vararg{Symbol}}

When calling the function solve, the user can provide a description of the method to use to solve the optimal control problem. The description can be a partial description or a full description. The function solve will find the best match from the available methods, thanks to the function getFullDescription. Then, the description is cleaned by the function clean to remove the Symbols that are specific to OptimalControl.jl and so must not be passed to the solver. For instance, the Symbol :direct is specific to OptimalControl.jl and must be removed. It must not be passed to the CTDirect.jl solver.