Remove unused aliases from DataTransformers.

test/decentralised_book_index/sync/data_transformers/author_transformer_test.exs

@@ -2,7 +2,6 @@ defmodule DecentralisedBookIndex.Sync.DataTransformers.AuthorTransformerTest do
   use ExUnit.Case, async: true
 
   alias DecentralisedBookIndex.Sync.DataTransformers.AuthorTransformer
-  alias DecentralisedBookIndex.Metadata.Author
 
   describe "correct transformations" do
     test "a json contains correct author information" do

test/decentralised_book_index/sync/data_transformers/book_transformer_test.exs

@@ -2,7 +2,6 @@ defmodule DecentralisedBookIndex.Sync.DataTransformers.BookTransformerTest do
   use ExUnit.Case, async: true
 
   alias DecentralisedBookIndex.Sync.DataTransformers.BookTransformer
-  alias DecentralisedBookIndex.Metadata.Book
 
   describe "correct transformations" do
     test "a json contains correct book information" do

test/decentralised_book_index/sync/data_transformers/publisher_transformer_test.exs

@@ -2,7 +2,6 @@ defmodule DecentralisedBookIndex.Sync.DataTransformers.PublisherTransformerTest
   use ExUnit.Case, async: true
 
   alias DecentralisedBookIndex.Sync.DataTransformers.PublisherTransformer
-  alias DecentralisedBookIndex.Metadata.Publisher
 
   describe "correct transformations" do
     test "a json contains correct publisher information" do