dispose method
Free the plugin resources associated with this ad.
Disposing a banner ad that's been shown removes it from the screen. Interstitial ads can't be programmatically removed from view.
Implementation
Future<bool> dispose() {
assert(_allAds[id] != null);
_allAds[id] = null;
return _invokeBooleanMethod('disposeAd', <String, dynamic>{'id': id});
}