[BucketOp] Delete and get behaviour in case of non-existent keys

In Eventing, when one tries to delete a key which doesn’t exist from a bucket, we throw an exception. This isn’t the case one tries to delete a key from JS object. Thus, we have different behaviour in the language for the same operator.

As per the standard, none of these 2 operations throw exceptions when dealing with non-existent keys. “get” will return undefined if the key doesn’t exist. This is a bug as we should stay consistent with the host language as far as possible, and there is no good reason to deviate here.

 We may need to ensure backwards compatibility (MB-35944)