Correct the ownership passing semantics of object::createBinary and make them explicit in the type system.

createBinary documented that it destroyed the parameter in error cases,
though by observation it does not. By passing the unique_ptr by value
rather than lvalue reference, callers are now explicit about passing
ownership and the function implements the documented contract. Remove
the explicit documentation, since now the behavior cannot be anything
other than what was documented, so it's redundant.

Also drops a unique_ptr::release in llvm-nm that was always run on a
null unique_ptr anyway.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213557 91177308-0d34-0410-b5e6-96231b3b80d8