Revert mistakes in "Better explanation of preparation" (#538)

* Revert "Better explanation of preparation (#536)"

This reverts commit 4d39e77.

* Fix

Author: gdalle

DifferentiationInterface/ext/DifferentiationInterfaceEnzymeExt/forward_onearg.jl

@@ -117,8 +117,8 @@ end
 function DI.prepare_gradient(
     f::F, backend::AutoEnzyme{<:ForwardMode,<:Union{Nothing,Const}}, x
 ) where {F}
-    valB = pick_batchsize(backend, length(x))
-    shadows = create_shadows(valB, x)
+    B = pick_batchsize(backend, length(x))
+    shadows = create_shadows(Val(B), x)
     return EnzymeForwardGradientPrep{B,typeof(shadows)}(shadows)
 end
 
@@ -180,8 +180,8 @@ function DI.prepare_jacobian(
     f::F, backend::AutoEnzyme{<:Union{ForwardMode,Nothing},<:Union{Nothing,Const}}, x
 ) where {F}
     y = f(x)
-    valB = pick_batchsize(backend, length(x))
-    shadows = create_shadows(valB, x)
+    B = pick_batchsize(backend, length(x))
+    shadows = create_shadows(Val(B), x)
     return EnzymeForwardOneArgJacobianPrep{B,typeof(shadows)}(shadows, length(y))
 end
 

DifferentiationInterface/ext/DifferentiationInterfaceEnzymeExt/reverse_onearg.jl

@@ -349,15 +349,11 @@ end
 
 struct EnzymeReverseOneArgJacobianPrep{Sy,B} <: JacobianPrep end
 
-function EnzymeReverseOneArgJacobianPrep(::Val{Sy}, ::Val{B}) where {Sy,B}
-    return EnzymeReverseOneArgJacobianPrep{Sy,B}()
-end
-
 function DI.prepare_jacobian(f::F, backend::AutoEnzyme{<:ReverseMode,Nothing}, x) where {F}
     y = f(x)
     Sy = size(y)
-    valB = pick_batchsize(backend, prod(Sy))
-    return EnzymeReverseOneArgJacobianPrep(Val(Sy), valB)
+    B = pick_batchsize(backend, prod(Sy))
+    return EnzymeReverseOneArgJacobianPrep{Sy,B}()
 end
 
 function DI.jacobian(