When a derived class does not inherit a designated initializer from
its base class, we override the designated initializer's vtable
entry with a stub which traps with a fatal error.
The stub cannot be called and clients do not need to be aware of
its existence, so don't print it at all in the module interface.
Fixes rdar://problem/71122015 / https://bugs.swift.org/browse/SR-13832.
