Remove references to the 'depends' property outside of Task.cpp

With the exception of `taskDifferences` and `taskInfoDifferences`,
deferred to #2572.

src/main.h

@@ -59,8 +59,6 @@ std::string colorizeError (const std::string&);
 std::string colorizeDebug (const std::string&);
 
 // dependency.cpp
-std::vector <Task> dependencyGetBlocked (const Task&);
-std::vector <Task> dependencyGetBlocking (const Task&);
 bool dependencyIsCircular (const Task&);
 void dependencyChainOnComplete (Task&);
 void dependencyChainOnStart (Task&);