chore(portal): remove unused file_size dep (#10547)

This doesn't appear to be used anywhere and eliminates one compile
warning due to the seemingly unmaintained
[sizeable](https://github.com/arvidkahl/sizeable) dep.

elixir/apps/web/mix.exs

@@ -71,7 +71,6 @@ defmodule Web.MixProject do
 
       # Other deps
       {:jason, "~> 1.2"},
-      {:file_size, "~> 3.0.1"},
       {:nimble_csv, "~> 1.2"},
 
       # Test deps