Pass down documented kwargs in structural_simplifiy

I didn't let the tests run because I thought it was a harmless doc change, I missed that these kwargs were pulled out. But at least the failure wasn't released.

src/systems/systems.jl

@@ -21,7 +21,9 @@ function structural_simplify(
         sys::AbstractSystem, io = nothing; simplify = false, split = true,
         allow_symbolic = true, allow_parameter = true, conservative = false, fully_determined = true,
         kwargs...)
-    newsys′ = __structural_simplify(sys, io; simplify, kwargs...)
+    newsys′ = __structural_simplify(sys, io; simplify, 
+                allow_symbolic = true, allow_parameter = true, conservative = false, fully_determined = true,
+                kwargs...)
     if newsys′ isa Tuple
         @assert length(newsys′) == 2
         newsys = newsys′[1]