Remove unused docs_from_files

lib/ex_doc/retriever.ex

@@ -17,7 +17,8 @@ defmodule ExDoc.Retriever do
   def docs_from_dir(dir, config) when is_binary(dir) do
     files = Path.wildcard(Path.expand("*.beam", dir))
 
-    docs_from_files(files, config)
+    files
+    |> Enum.map(&filename_to_module/1)
     |> docs_from_modules(config)
   end
 
@@ -26,15 +27,6 @@ defmodule ExDoc.Retriever do
     |> sort_modules(config)
   end
 
-  @doc """
-  Extract documentation from all modules in the specified list of files
-  """
-  @spec docs_from_files([Path.t()], ExDoc.Config.t()) :: [ExDoc.ModuleNode.t()]
-  def docs_from_files(files, _config) when is_list(files) do
-    files
-    |> Enum.map(&filename_to_module(&1))
-  end
-
   @doc """
   Extract documentation from all modules in the list `modules`
   """