Call __del() before remove()

Call __del() before remove()

The "remove" event for collections is now called before the item is removed
in the case of the ``collection.remove()`` method, as is consistent with the
behavior for most other forms of collection item removal (such as
``__delitem__``, replacement under ``__setitem__``).  The ``pop()`` methods
are now the only exception as the target item is not available until after
the pop operation proceeds.

This allows ``remove()`` to be consistent in its behavior with all
the other collection operations, allows the "before_delete" hook
to be local to "pop()" operations only, and removes some method overhead.

We are also looking here to gain some more predictability in terms
of the fix for #1103.

Change-Id: I4fdea911517d65cc300fae0e9c351a471e52e4ab