title: remove unused preprocessor symbols in c# binary
body: <p>I have a project with a few conditional builds.  I compiled it. And then used dotpeek to look at it. I noticed <em>ALL</em> conditional statements and the code that it wraps even when not defined. </p>
  
  <p>Since this app is modified in some key ways for different clients, I would like a build for that client have a binary that <em>ONLY</em> contains the active #ifs that have been defined. </p>
  
  <p>How can I do an automated build that achieves this?</p>