fix: remove dead code

Author: gdalle

DifferentiationInterface/src/first_order/pushforward.jl

@@ -310,11 +310,7 @@ function _prepare_pushforward_aux(
     contexts::Vararg{Context,C};
 ) where {F,C}
     _sig = signature(f!, y, backend, x, tx, contexts...; strict)
-    dy = if y isa Number
-        oneunit(y)
-    else
-        basis(y)
-    end
+    dy = basis(y)
     pullback_prep = prepare_pullback_nokwarg(strict, f!, y, backend, x, (dy,), contexts...)
     return PullbackPushforwardPrep(_sig, pullback_prep)
 end