delete increment-version.js.

incrementing a dev bundle version is easy.

incrementing the release version is no longer necessary. the relevant files
consist of:

 - things that are really engine version (which is autogenerated from a hash)
 - the curl install script (which is also really engine version and is part
   of release blessing now)
 - debian/rpm stuff (going away)
 - docs app (which now uses Meteor.release)
 - manifest.json (the one place you do need to bump to do a release, but
   this can be done manually)