Allow removing a whole XML element using <config-file>

Currently, <config-file> can only add an XML element to a config file, but not remove an element. <edit-config> can remove attributes from an element, but not whole elements.

I'd like the ability to remove elements by adding something to config.xml instead of writing a hook.

This is useful because some plugins include extra permissions which are not always needed (For example, cordova-plugin-file adds the WRITE_EXTERNAL_STORAGE permission, but not all apps that include cordova-plugin-file will actually write outside their data directory).

Example syntax:

<config-file mode="remove" parent="/manifest" target="AndroidManifest.xml" xmlns:android="http://schemas.android.com/apk/res/android">
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
</config-file>

(Note the mode="remove", the default if absent should be "add")