CB-5105 Removed dead code for device.version

Dead code has been removed from the native side for the following
platforms:

-Android
-WP8
-BB10
-Windows 8
Every variable, method or argument related with retrieve the cordova
version from the native side has been removed. Given the fact that
cordova.js, it's providing the cordova.version.

The plugin has been tested under each platform involved with the
expected results, everything settled to be added to the repository.

github: close #13