Remove SupportPress remnants

As of r16882-dotorg the SupportPress configs and externals have been removed.

Can you please:
* Remove the SupportPress nginxNGINX NGINX is open source software for web serving, reverse proxying, caching, load balancing, media streaming, and more. It started out as a web server designed for maximum performance and stability. In addition to its HTTP server capabilities, NGINX can also function as a proxy server for email (IMAP, POP3, and SMTP) and a reverse proxy and load balancer for HTTP, TCP, and UDP servers. config file from wporg-web
* Remove the public_html/sp directory from all hosts (production & sandbox). Due to nested externals, there’s a set of */includes/backpress* directories that SVNSVN Apache Subversion (often abbreviated SVN, after its command name svn) is a software versioning and revision control system. Software developers use Subversion to maintain current and historical versions of files such as source code, web pages, and documentation. Its goal is to be a mostly compatible successor to the widely used Concurrent Versions System (CVS). WordPress core and the released code are all centrally managed through SVN. won’t clean up and will leave as a local mod (I couldn’t work around it due to nested externals within nested externals)