remove dependency on bst

demo/rank/mq2008.conf

@@ -5,13 +5,13 @@ objective="rank:pairwise"
 
 # Tree Booster Parameters
 # step size shrinkage
-bst:eta = 0.1 
+eta = 0.1 
 # minimum loss reduction required to make a further partition
-bst:gamma = 1.0 
+gamma = 1.0 
 # minimum sum of instance weight(hessian) needed in a child
-bst:min_child_weight = 0.1
+min_child_weight = 0.1
 # maximum depth of a tree
-bst:max_depth = 6
+max_depth = 6
 
 # Task parameters
 # the number of round to do boosting