AST: Remove dead code from RecordLayoutBuilder

No functionality change intended.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@220005 91177308-0d34-0410-b5e6-96231b3b80d8
CodeGen: Kill FillInNullDataMemberPointers

It exists to handle the case where base subobjects are character arrays.
This never happens.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@220006 91177308-0d34-0410-b5e6-96231b3b80d8