As you've discovered, simply deleting Server.app doenlsnt undo the Lion to Lion Server conversion process. The first time Server.app ran, it used Software Update to download additional server essentials from Apple in order to perform what was designed to be a one-way conversion. (For those familiar with how Mac OS X Server installers were put together, the basic "client" version of Lion already includes the server essentials like servermgrd.)
As Apple suggests, you can turn off the performance dedications for server processes. However, you still need to stop each service individually using Server.app, Server Admin, the serveradmin command, or by stopping each process required by each service with webappctl, apachectl, or launchctl, etc.
However, even turning off services does not completely revert Lion Server to the vanilla Lion state. Deleting the server version property list file only makes Mac OS X say "Mac OS X" instead of "Mac OS X Server."
If you want to absolutely remove all if the server components, the easiest thing to do is to restore a backup of the computer from before you made the switch, or to reinstall Lion.