Remove unused partition check code

This code is unused and was disabled in BTC core and then deleted,
since it didn't work correctly: https://github.com/bitcoin/bitcoin/pull/8275

src/main.h

@@ -239,8 +239,7 @@ bool ProcessMessages(CNode* pfrom);
 bool SendMessages(CNode* pto, bool fSendTrickle);
 /** Run an instance of the script checking thread */
 void ThreadScriptCheck();
-/** Try to detect Partition (network isolation) attacks against us */
-void PartitionCheck(bool (*initialDownloadCheck)(), CCriticalSection& cs, const CBlockIndex *const &bestHeader, int64_t nPowTargetSpacing);
+
 /** Check whether we are doing an initial block download (synchronizing from disk or network) */
 bool IsInitialBlockDownload();
 /** Check if the daemon is in sync, if not, it returns 1 or if due to best header only, the difference in best