Bug 1050416 - [Messages][Build] Add build script to ignore the desktop-only folder for production build. r=schung

* Added build script to delete desktop-only folder;
* Removed desktop-only "if"s from code;
* Changed way of loading desktop-only shims
I wonder if we can not just do "if (navigator.mozIccManager)" in the failing code instead of adding this...

In the simulator, I'm adding a more complex mock (but from the outside) so that we can control the DSDS settings, but for the nominal case I wonder if this is needed for the nominal case