Fixed deduplicated files from orphan media being deleted as well

Happens when a file is uploaded, then orphaned, and a similar file is
used somewhere. The CleanMedia job service didn't consider that case

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/mobilizon/storage/custom_functions.ex

@@ -0,0 +1,10 @@
+defmodule Mobilizon.Storage.CustomFunctions do
+  @moduledoc """
+  Helper module for custom PostgreSQL functions
+  """
+  defmacro split_part(string, delimiter, position) do
+    quote do
+      fragment("split_part(?, ?, ?)", unquote(string), unquote(delimiter), unquote(position))
+    end
+  end
+end