[t:3096], some cleanup, get rid of cursor->oldest_living_xid, not necessary

git-svn-id: file:///svn/toku/tokudb@33839 c7de825b-a66e-492c-adef-691d508d4ae1

newbrt/brt-internal.h

@@ -561,7 +561,6 @@ struct brt_cursor {
     DBT key, val;             // The key-value pair that the cursor currently points to
     DBT range_lock_left_key, range_lock_right_key;
     BOOL left_is_neg_infty, right_is_pos_infty;
-    TXNID      oldest_living_xid;// what was the oldest live txnid when we created the cursor?
     BOOL is_snapshot_read; // true if query is read_committed, false otherwise
     BOOL is_leaf_mode;
     TOKUTXN ttxn;

newbrt/brt.c

@@ -4871,7 +4871,6 @@ int toku_brt_cursor (
     toku_init_dbt(&cursor->range_lock_right_key);
     cursor->left_is_neg_infty = FALSE;
     cursor->right_is_pos_infty = FALSE;
-    cursor->oldest_living_xid = ttxn ? toku_logger_get_oldest_living_xid(ttxn->logger, NULL) : TXNID_NONE;
     cursor->is_snapshot_read = is_snapshot_read;
     cursor->is_leaf_mode = FALSE;
     cursor->ttxn = ttxn;