NPE in ConfigInstaller on ConfigDelete

The ConfigInstaller is handling a Config Delete Event now, but it always throws a NullPointException which crowds up the logs.

On delete, the ConfigInstaller tries to get the corresponding Configuration object: https://github.com/apache/felix/blob/trunk/fileinstall/src/main/java/org/apache/felix/fileinstall/internal/ConfigInstaller.java#L176

It's never going to get the Configuration object because it was just deleted. So the getConfiguration call creates a new one with null as the properties. Then on line 180 there is a NullPointerException.

Unfortunately, the fix for this will require changing the ConfigurationListener API so that the ConfigurationEvent either has the whole Dictionary of configuration properties or at least the felix.file.install property, if it exists.