[analyzer] Remove incorrect workaround for unimplemented temporary destructors.

If we're trying to get the zero element region of something that's not a region,
we should be returning UnknownVal, which is what ProgramState::getLValue will
do for us.

Patch by Alex McCarthy!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@205327 91177308-0d34-0410-b5e6-96231b3b80d8