Remove unreliable storage test

We wait for the storage process to finish writing the table to file
and then read the file manually, however the storage may be writing
to the file again (and the writing is async), so we may try to read
a partially written file.

test/livebook/storage_test.exs

@@ -102,41 +102,4 @@ defmodule Livebook.StorageTest do
       assert [] = Storage.all(:unknown_namespace)
     end
   end
-
-  describe "persistence" do
-    defp read_table_and_lookup(entity) do
-      Process.sleep(1)
-
-      # :ets.tab2file is asynchronous and may occasionally take
-      # longer, so we retry
-      {:ok, tab} =
-        with {:error, _} <- read_table(),
-             :ok <- Process.sleep(100),
-             {:error, _} <- read_table(),
-             :ok <- Process.sleep(1000) do
-          read_table()
-        end
-
-      :ets.lookup(tab, {:persistence, entity})
-    end
-
-    defp read_table() do
-      Storage.config_file_path()
-      |> String.to_charlist()
-      |> :ets.file2tab()
-    end
-
-    test "insert triggers saving to file" do
-      :ok = Storage.insert(:persistence, "insert", key: "val")
-
-      assert [_test] = read_table_and_lookup("insert")
-    end
-
-    test "delete triggers saving to file" do
-      :ok = Storage.insert(:persistence, "delete", key: "val")
-      :ok = Storage.delete(:persistence, "delete")
-
-      assert [] = read_table_and_lookup("delete")
-    end
-  end
 end