MS ABI: Remove a useless FileCheck line

1. CHECK-NOT-LABEL is not valid FileCheck.
2. This test would not trigger the CHECK-NOT-LABEL even if 'interface' is
   replaced with 'struct'.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@201462 91177308-0d34-0410-b5e6-96231b3b80d8