README: Remove note about requiring cabal files

We are using patches exclusively now for the sake of simplicity.

README.md

@@ -17,10 +17,6 @@ existing Hackage package(s).
   as one of the main purposes of these patches is to make regression
   testing possible. I.e. try to avoid conditional compilation.
 
-- If only the `.cabal` file needs to be modified, a `.cabal` file
-  SHOULD be used instead of a `.patch` file. If the changes to the
-  `.cabal` file are too invasive (e.g. removing modules, changing the
-  structure of the package etc), a `.patch` file must be used.
 
 ## How this works