refactor: move CBlockIndex#ToString() from header to implementation

which allows dropping tinyformat.h from the header file.

src/chain.cpp

@@ -4,6 +4,7 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <chain.h>
+#include <tinyformat.h>
 #include <util/time.h>
 
 std::string CBlockFileInfo::ToString() const
@@ -11,6 +12,12 @@ std::string CBlockFileInfo::ToString() const
     return strprintf("CBlockFileInfo(blocks=%u, size=%u, heights=%u...%u, time=%s...%s)", nBlocks, nSize, nHeightFirst, nHeightLast, FormatISO8601Date(nTimeFirst), FormatISO8601Date(nTimeLast));
 }
 
+std::string CBlockIndex::ToString() const
+{
+    return strprintf("CBlockIndex(pprev=%p, nHeight=%d, merkle=%s, hashBlock=%s)",
+                     pprev, nHeight, hashMerkleRoot.ToString(), GetBlockHash().ToString());
+}
+
 void CChain::SetTip(CBlockIndex *pindex) {
     if (pindex == nullptr) {
         vChain.clear();

src/chain.h

@@ -11,7 +11,6 @@
 #include <flatfile.h>
 #include <primitives/block.h>
 #include <sync.h>
-#include <tinyformat.h>
 #include <uint256.h>
 
 #include <vector>
@@ -302,13 +301,7 @@ public:
         return pbegin[(pend - pbegin) / 2];
     }
 
-    std::string ToString() const
-    {
-        return strprintf("CBlockIndex(pprev=%p, nHeight=%d, merkle=%s, hashBlock=%s)",
-            pprev, nHeight,
-            hashMerkleRoot.ToString(),
-            GetBlockHash().ToString());
-    }
+    std::string ToString() const;
 
     //! Check whether this block index entry is valid up to the passed validity level.
     bool IsValid(enum BlockStatus nUpTo = BLOCK_VALID_TRANSACTIONS) const