Use only kernel/coinstats.h in index/coinstatsindex.h

Removes a circular dependency, horray!

src/index/coinstatsindex.h

@@ -9,7 +9,7 @@
 #include <crypto/muhash.h>
 #include <flatfile.h>
 #include <index/base.h>
-#include <node/coinstats.h>
+#include <kernel/coinstats.h>
 
 /**
  * CoinStatsIndex maintains statistics on the UTXO set.

test/lint/lint-circular-dependencies.py

@@ -14,7 +14,6 @@ import sys
 EXPECTED_CIRCULAR_DEPENDENCIES = (
     "chainparamsbase -> util/system -> chainparamsbase",
     "node/blockstorage -> validation -> node/blockstorage",
-    "index/coinstatsindex -> node/coinstats -> index/coinstatsindex",
     "policy/fees -> txmempool -> policy/fees",
     "qt/addresstablemodel -> qt/walletmodel -> qt/addresstablemodel",
     "qt/recentrequeststablemodel -> qt/walletmodel -> qt/recentrequeststablemodel",