IR: remove dead code

This was added in r134994, to fix a memory leak;
three days later, r135248 switched
ContainedTys from being new-allocated to being allocated
via BumpPtrAllocator, and the earlier fix was never
reverted.

The destructor doesn't seem to ever actually be called
on Types anyway, so it's harmless, but if it were,
this'd be an invalid pointer.

This reverts r134994.

llvm-svn: 216354