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>

incorporealcms/markdown.py

@@ -135,11 +135,6 @@ def handle_markdown_file_path(path: str, pages_root: str) -> str:
     extra_footer = get_meta_str(md, 'footer') if md.Meta.get('footer') else None
     template_name = get_meta_str(md, 'template') if md.Meta.get('template') else 'base.html'
 
-    # check if this has a HTTP redirect
-    redirect_url = get_meta_str(md, 'redirect') if md.Meta.get('redirect') else None
-    if redirect_url:
-        raise NotImplementedError("redirects in markdown are unsupported!")
-
     template = jinja_env.get_template(template_name)
     return template.render(title=page_title,
                            config=Config,