Retry defaulting the virtual dtor in LoadedObjectInfo

Originally committed in r237975, GCC 4.7 gave a compilation error
regarding "looser throw specification" though it seemed to be pointing
to a virtual defaulted dtor in a base class and an override defaulted
dtor in a derived class - so I'm not quite sure why/how they could end
up with different throw specifications. To simplify and reduce the risk
of this, I've just removed the pointless override in the derived class,
the base class's should be sufficient. *fingers crossed*

llvm-svn: 239088