fix: remove jac/tgrad cache-related code

Author: AayushSabharwal

src/systems/abstractsystem.jl

@@ -899,27 +899,6 @@ end
 
 has_equations(::AbstractSystem) = true
 
-const EMPTY_TGRAD = Vector{Num}(undef, 0)
-const EMPTY_JAC = Matrix{Num}(undef, 0, 0)
-function invalidate_cache!(sys::AbstractSystem)
-    if has_tgrad(sys)
-        get_tgrad(sys)[] = EMPTY_TGRAD
-    end
-    if has_jac(sys)
-        get_jac(sys)[] = EMPTY_JAC
-    end
-    if has_ctrl_jac(sys)
-        get_ctrl_jac(sys)[] = EMPTY_JAC
-    end
-    if has_Wfact(sys)
-        get_Wfact(sys)[] = EMPTY_JAC
-    end
-    if has_Wfact_t(sys)
-        get_Wfact_t(sys)[] = EMPTY_JAC
-    end
-    return sys
-end
-
 function Setfield.get(obj::AbstractSystem, ::Setfield.PropertyLens{field}) where {field}
     getfield(obj, field)
 end