[BUG #6965] Mobile Skeleton: Remove Dependency from qx/mobile/icon/<theme> Resources

* Removed unused qx.Mobile theming icons.
* Moved spinner and checkbox as Base64 icons directly to css.
[BUG #6965] Mobile Skeleton: Remove Dependency from qx/mobile/icon/<theme> Resources

* Removed "qx.mobile.platform" variable out of config.json
[BUG #6965] Mobile Skeleton: Remove Dependency from qx/mobile/icon/<theme> Resources

* Removed deleted icon assets.
[BUG #6965] Mobile Skeleton: Remove Dependency from qx/mobile/icon/<theme> Resources

* Moved spinner icon as Base64 to css.