Remove useless empty *Private classes

Several recent commits ported CodeModel, Importers, Uses and Definitions
to LockedItemRepository::op pattern. These commits made the
corresponding private classes empty and d-pointers redundant. KDevelop's
binary compatibility is not very important, while the code is shorter
and simpler now. The private classes are unlikely to be resurrected any
time soon.

Disable copying and moving these classes as they are meant to be
singletons. Copy and move operations were deleted before this commit due
to QScopedPointer d_ptr data members, which are now gone.