Chore: Remove duplicate and unreferenced test sample files

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/paperless/tests/samples/mail/sample.html

@@ -1,19 +0,0 @@
- <html>
-    <head>
-      <meta http-equiv="content-type" content="text/html; charset=UTF-8">
-    </head>
-    <body>
-      <p>Some Text</p>
-      <p>
-				<img src="cid:part1.pNdUSz0s.D3NqVtPg@example.de" alt="Has to be rewritten to work..">
-				<img src="http://localhost:8080/assets/logo_full_white.svg" alt="This image should not be shown.">
-			</p>
-
-      <p>and an embedded image.<br>
-      </p>
-      <p id="changeme">Paragraph unchanged.</p>
-      <scRipt>
-          document.getElementById("changeme").innerHTML = "Paragraph changed via Java Script.";
-      </script>
-    </body>
-  </html>