Remove uncovered code [skip ci]

Author: adamtheturtle

tests/mock_vws/utils/__init__.py

@@ -449,12 +449,14 @@ def make_image_file(
     """
     image_buffer = io.BytesIO()
     image = Image.new(color_space, (width, height))
-    if color_space != 'L':
-        reds = random.choices(population=range(0, 255), k=width * height)
-        greens = random.choices(population=range(0, 255), k=width * height)
-        blues = random.choices(population=range(0, 255), k=width * height)
-        pixels = list(zip(reds, greens, blues))
-        image.putdata(pixels)
+    # If this assertion ever fails, see
+    # https://github.com/adamtheturtle/vws-test-fixtures for what to do.
+    assert color_space != 'L'
+    reds = random.choices(population=range(0, 255), k=width * height)
+    greens = random.choices(population=range(0, 255), k=width * height)
+    blues = random.choices(population=range(0, 255), k=width * height)
+    pixels = list(zip(reds, greens, blues))
+    image.putdata(pixels)
     image.save(image_buffer, file_format)
     image_buffer.seek(0)
     return image_buffer