There's only one user of the various `DIObjCProperty::is*Property()`
accessors -- `DwarfUnit::constructTypeDIE()` -- and it's just using the
reverse logic to reconstruct the bitfield. Drop this API and simplify
the only caller.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234818 91177308-0d34-0410-b5e6-96231b3b80d8