determined from flag == BTR_CUR_ABORTED.  This flag value was previously
never tested for.  It was only assigned to, in the only place where
leaf_in_buf_pool would be set FALSE.

btr_cur_search_to_nth_level(): Do not initialize cursor->leaf_in_buf_pool.

btr_pcur_was_buffered(): Remove.  The only caller, row_search_index_entry(),
will switch (cursor->flag) and handle BTR_CUR_ABORTED as well.

row_purge_remove_sec_if_poss_low(): Remove the assertions on leaf_in_buf_pool.