Now that all of the derived types have disciplined interfaces, we can eliminate

Now that all of the derived types have disciplined interfaces, we can eliminate
all of the ad-hoc storage of contained types.  This allows getContainedType to
not be virtual, and allows us to entirely delete the TypeIterator class.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@11230 91177308-0d34-0410-b5e6-96231b3b80d8