Remove second argument of model destroyed event

[ricardograca]

• Related Issues: Second argument to model destroyed event is useless #1722
• Previous PRs: Fix documentation of some events #1723

Introduction

In #1723 it was discovered that the second argument to the destroyed event was completely useless, so this just removes it.

Motivation

There is no point in having that argument as it will always have the same value. See the above linked related issue for more info.

Fixes #1722.

Current PR Issues

This is a breaking change in case someone is using the current third argument (options) for something in this event's handler. This is highly unlikely, so the disruption should be minimal or non-existent.