validation: Remove unused boost interruption_point

ActivateBestChain (ABC) is only called in the "msghand" or one of the
RPC threads, neither of which is a boost::thread. However, ABC is also
called in ThreadImport (which currently happens to be a boost::thread).
In all cases, the interruption_point is redundant with the breakpoint in
ABC that triggers when ShutdownRequested()

VerifyDB is only called in the main thread ("init") or one of the RPC
threads, neither of which is a boost::thread.

Author: MarcoFalke

src/validation.cpp

@@ -50,7 +50,6 @@
 #include <string>
 
 #include <boost/algorithm/string/replace.hpp>
-#include <boost/thread.hpp>
 
 #if defined(NDEBUG)
 # error "Bitcoin cannot be compiled without assertions."
@@ -2859,8 +2858,6 @@ bool CChainState::ActivateBestChain(BlockValidationState &state, const CChainPar
     CBlockIndex *pindexNewTip = nullptr;
     int nStopAtHeight = gArgs.GetArg("-stopatheight", DEFAULT_STOPATHEIGHT);
     do {
-        boost::this_thread::interruption_point();
-
         // Block until the validation queue drains. This should largely
         // never happen in normal operation, however may happen during
         // reindex, causing memory blowup if we run too far ahead.
@@ -2929,8 +2926,7 @@ bool CChainState::ActivateBestChain(BlockValidationState &state, const CChainPar
         // never shutdown before connecting the genesis block during LoadChainTip(). Previously this
         // caused an assert() failure during shutdown in such cases as the UTXO DB flushing checks
         // that the best block hash is non-null.
-        if (ShutdownRequested())
-            break;
+        if (ShutdownRequested()) break;
     } while (pindexNewTip != pindexMostWork);
     CheckBlockIndex(chainparams.GetConsensus());
 
@@ -4272,7 +4268,6 @@ bool CVerifyDB::VerifyDB(const CChainParams& chainparams, CCoinsView *coinsview,
     int reportDone = 0;
     LogPrintf("[0%%]..."); /* Continued */
     for (pindex = ::ChainActive().Tip(); pindex && pindex->pprev; pindex = pindex->pprev) {
-        boost::this_thread::interruption_point();
         const int percentageDone = std::max(1, std::min(99, (int)(((double)(::ChainActive().Height() - pindex->nHeight)) / (double)nCheckDepth * (nCheckLevel >= 4 ? 50 : 100))));
         if (reportDone < percentageDone/10) {
             // report every 10% step
@@ -4330,7 +4325,6 @@ bool CVerifyDB::VerifyDB(const CChainParams& chainparams, CCoinsView *coinsview,
     // check level 4: try reconnecting blocks
     if (nCheckLevel >= 4) {
         while (pindex != ::ChainActive().Tip()) {
-            boost::this_thread::interruption_point();
             const int percentageDone = std::max(1, std::min(99, 100 - (int)(((double)(::ChainActive().Height() - pindex->nHeight)) / (double)nCheckDepth * 50)));
             if (reportDone < percentageDone/10) {
                 // report every 10% step