Fix includes and add some comments

graph/scc.h

@@ -21,7 +21,6 @@ private:
   // Each SCC has a representative vertex that helps
   // answer strong connectivity queries in O(1) time
   T proxy;
-
 };
 
 }; // namespace graph

graph/transitive_closure.h

@@ -1,18 +0,0 @@
-#ifndef TRANSITIVE_CLOSURE_H_
-#define TRANSITIVE_CLOSURE_H_
-
-#include "digraph.h"
-
-namespace graph {
-
-// Transitive closure matrix class to answer reachability queries
-template<typename T>
-class TransitiveClosure {
-public:
-  TransitiveClosure() = default;
-};
-
-} // namespace graph
-
-
-#endif