Remove default versionCode and CFBundleVersion from manifest.mobile.json

After 0749521 CCA uses cordova's code path for dealing with versionCode and
CFBundleVersion. Cordova will use the following defaults if versionCode and
CFBundleVersion are not explicitly provided:

* CFBundleVersion = version (excluding any rc tags after a dash)
* versionCode = (major*100 + minor)*100 + rev. (assuming version = major.minor.rev-whatever)

The defaults are currently computed in
https://github.com/apache/cordova-lib/blob/master/cordova-lib/src/cordova/metadata/android_parser.js#L362
https://github.com/apache/cordova-lib/blob/master/cordova-lib/src/cordova/metadata/ios_parser.js#L260