Tweak deletion, emit CatchDeletion() only once

Tweak deletion, emit CatchDeletion() only once

Parent class d'tor runs after derived class d'tor. By the time
~TimeAxisView() is called, the actual object has already been
deleted and dyanamic_cast<RouteTimeAxisView*> or
dynamic_cast<AutomationTimeAxisView*> will fail.

CatchDeletion() needs to be emitted from the actual d'tor of the object.

There are currently three non-virtual TAVs:
 * RouteTimeAxisView
 * AutomationTimeAxisView
 * VCATimeAxisView

The first two already directly emit CatchDeletion(), there's no need to
call it again from ~TimeAxisView().