refactor: remove __structural_simplify(::JumpSystem)

Author: AayushSabharwal

Diff for: src/systems/systems.jl

@@ -56,10 +56,6 @@ function structural_simplify(
     end
 end
 
-function __structural_simplify(sys::JumpSystem, args...; kwargs...)
-    return sys
-end
-
 function __structural_simplify(sys::AbstractSystem, io = nothing; simplify = false,
         kwargs...)
     # TODO: convert noise_eqs to brownians for simplification