Take out tree_depth from temporary index because it never gets used

Author: xchang1

bdsg/include/bdsg/snarl_distance_index.hpp

@@ -1503,7 +1503,6 @@ class SnarlDistanceIndex : public SnarlDecomposition, public TriviallySerializab
             handlegraph::nid_t end_node_id;
             bool end_node_rev;
             size_t end_node_length=0;
-            size_t tree_depth = 0;
             //Type of the parent and offset into the appropriate vector
             //(TEMP_ROOT, 0) if this is a root level chain
             pair<temp_record_t, size_t> parent;
@@ -1543,7 +1542,6 @@ class SnarlDistanceIndex : public SnarlDecomposition, public TriviallySerializab
             size_t min_length = std::numeric_limits<size_t>::max(); //Not including boundary nodes
             size_t max_length = 0;
             size_t max_distance = 0;
-            size_t tree_depth = 0;
             pair<temp_record_t, size_t> parent;
             vector<pair<temp_record_t, size_t>> children; //All children, nodes and chains, in arbitrary order
             unordered_set<size_t> tippy_child_ranks; //The ranks of children that are tips