Make it clear that drop_deinit cannot be used to prevent a deinit called from a destroy_addr.
This is more a refactoring and clarification than a bug fix, because a destroy_addr cannot have a drop_deinit as operand, anyway.
In regular swift this is a nice optimization. In embedded swift it's a requirement, because the compiler needs to be able to specialize generic deinits of non-copyable types.
The new de-virtualization utilities are called from two places:
* from the new DeinitDevirtualizer pass. It replaces the old MoveOnlyDeinitDevirtualization, which is very basic and does not fulfill the needs for embedded swift.
* from MandatoryPerformanceOptimizations for embedded swift
