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/node/miner.cpp

@@ -167,7 +167,7 @@ std::unique_ptr<CBlockTemplate> BlockAssembler::CreateNewBlock(const CScript& sc
     pblocktemplate->vTxSigOpsCost[0] = WITNESS_SCALE_FACTOR * GetLegacySigOpCount(*pblock->vtx[0]);
 
     BlockValidationState state;
-    if (!TestBlockValidity(state, chainparams, m_chainstate, *pblock, pindexPrev, false, false)) {
+    if (!TestBlockValidity(state, chainparams, m_chainstate, *pblock, pindexPrev, GetAdjustedTime, false, false)) {
         throw std::runtime_error(strprintf("%s: TestBlockValidity failed: %s", __func__, state.ToString()));
     }
     int64_t nTime2 = GetTimeMicros();