make Return<T> non-copyable.

It doesn't make sense to copy a Return<T> object. Deleting the
copy constructor help reduce bugs in client code (so that they
won't call isOk() on the object and think they have checked
the status while they actually haven't done so.)

Test: make -j64
Change-Id: Ibef2d4da8820b484076f1d0ca6ac7ff67f39079b
1 file changed