Made 'rm' build option work if file doesn't exist
Made 'rm' build option work if file doesn't exist

The latest platform tools delete build.properties, the old ones didn't.
This allows several builds to work either way.

matlink/fdroidserver,f-droid/fdroidserver,fdroidtravis/fdroidserver,fdroidtravis/fdroidserver,pfalcon/fdroidserver,matlink/fdroidserver,f-droid/fdroidserver,OneEducation/AppUniverse_Server,pfalcon/fdroidserver,f-droid/fdroidserver,pfalcon/fdroidserver,pfalcon/fdroidserver,pfalcon/fdroidserver,f-droid/fdroid-server,f-droid/fdroidserver,fdroidtravis/fdroidserver,fantastico/fdroidserver,f-droid/fdroid-server,f-droid/fdroid-server,OneEducation/AppUniverse_Server,f-droid/fdroid-server,matlink/fdroidserver,fdroidtravis/fdroidserver,OneEducation/AppUniverse_Server,OneEducation/AppUniverse_Server,f-droid/fdroidserver,fantastico/fdroidserver,fantastico/fdroidserver,OneEducation/AppUniverse_Server,matlink/fdroidserver,f-droid/fdroid-server,fantastico/fdroidserver,matlink/fdroidserver,fantastico/fdroidserver