refactor: remove automatic code generation in DI (#789)

* refactor: remove automatic code generation in DI for better coverage stats

* Remove Aqua check

Author: gdalle

DifferentiationInterface/src/DifferentiationInterface.jl

@@ -61,9 +61,6 @@ include("second_order/second_derivative.jl")
 include("second_order/hvp.jl")
 include("second_order/hessian.jl")
 
-include("fallbacks/no_prep.jl")
-include("fallbacks/change_prep.jl")
-
 include("misc/differentiate_with.jl")
 include("misc/from_primitive.jl")
 include("misc/sparsity_detector.jl")