Fix docs

docs/source/backend/index.rst

@@ -16,7 +16,6 @@ who wish to customize or extend the behaviour of the code generator in their app
     iteration_space
     translation
     platforms
-    reduction_codegen
     transformations
     gpu_codegen
     errors

docs/source/user_manual/reductions.md

@@ -96,10 +96,7 @@ ps.inspect(kernel)
 
 :::{note}
 The generated reduction kernels may vary vastly for different platforms and optimizations.
-For the sake of compactness, the impact of different backend or optimization choices is left out.
-
-A detailed description of configuration choices and their impact on the generated code can be found in
-{ref}`codegen_reductions`.
+You can find a  detailed description of configuration choices and their impact on the generated code below.
 :::
 
 The kernel can be compiled and run immediately.