Remove old imghdr patch test (#143)

Test was designed to verify an old workaround when we were still using
imghdr. This workaround has been removed and there is no reason for it
to continue its existence in this universe...

tests/test_image.py

@@ -5,8 +5,6 @@
 from unittest import mock
 from xml.etree.ElementTree import ParseError as XMLParseError
 
-import filetype
-
 from willow.image import (
     AvifImageFile,
     BMPImageFile,
@@ -306,23 +304,3 @@ def test_optimize_with_an_actual_file(
             self.image.optimize(f, "jpeg")
         mock_process.assert_called_with("tests/images/people.jpg")
         mock_unlink.assert_not_called()
-
-
-class TestImghdrJPEGPatch(unittest.TestCase):
-    def test_detects_photoshop3_jpeg(self):
-        f = io.BytesIO()
-        f.write(b"\xff\xd8\xff\xed\x00,Photoshop 3.0\x00")
-        f.seek(0)
-
-        image_format = filetype.guess_extension(f)
-
-        self.assertEqual(image_format, "jpg")
-
-    def test_junk(self):
-        f = io.BytesIO()
-        f.write(b"Not an image")
-        f.seek(0)
-
-        image_format = filetype.guess_extension(f)
-
-        self.assertIsNone(image_format)