Add ChainstateManager::m_adjusted_time_callback

This decouples validation.cpp from netaddress.cpp (transitively,
timedata.cpp, and asmap.cpp).

This is important for libbitcoinkernel as:

- There is no reason for the consensus engine to be coupled with
  netaddress, timedata, and asmap
- Users of libbitcoinkernel can now easily supply their own
  std::function that provides the adjusted time.

See the src/Makefile.am changes for some satisfying removals.

src/bitcoin-chainstate.cpp

@@ -72,6 +72,7 @@ int main(int argc, char* argv[])
     // SETUP: Chainstate
     const ChainstateManager::Options chainman_opts{
         chainparams,
+        static_cast<int64_t(*)()>(GetTime),
     };
     ChainstateManager chainman{chainman_opts};