remove the broken/deprecated redirect tag support

when this project *wasn't* a SSG, it could serve up redirects, which is
something that was only rarely needed, and looking now, I don't do it at
all on any of my current sites, so I'm just going to remove the tiny bit
of code for it that remained in the SSG project

Signed-off-by: Brian S. Stephan <bss@incorporeal.org>

tests/test_markdown.py

@@ -103,12 +103,6 @@ def test_render_with_default_style_override():
                 in handle_markdown_file_path('index.md', PAGES_DIR)
 
 
-def test_redirects_error_unsupported():
-    """Test that we throw a warning about the barely-used Markdown redirect tag, which we can't support via SSG."""
-    with pytest.raises(NotImplementedError):
-        handle_markdown_file_path('redirect.md', os.path.join(INSTANCE_DIR, 'broken'))
-
-
 def test_instance_resource_path_to_request_path_on_index():
     """Test index.md -> /."""
     assert instance_resource_path_to_request_path('index.md') == '/'