Back out parts of the changes for 3c48d71c7f and b132281c11 weren't
necessary: a cursor search operation is required to (somehow) no longer
reference the application's key when it returns, and that's sufficient to
ensure a duplicated cursor no longer references the original cursor's key.

Replace the WT_CURSOR.dup_position function that copied the original
cursor's key with Memrata drive code that copies the cursor key (if the
operation itself isn't going to update it).
Remove last vestiges of the non-transactional implementation.