chainparams: move CCheckpointData into chainparams.h

This unties CChainParams from its dependency on checkpoints. Instead, now it
only depends on the raw checkpoint data.

src/checkpoints.h

@@ -10,6 +10,7 @@
 #include <map>
 
 class CBlockIndex;
+struct CCheckpointData;
 
 /**
  * Block-chain checkpoints are compiled-in sanity checks.
@@ -17,14 +18,6 @@ class CBlockIndex;
  */
 namespace Checkpoints
 {
-typedef std::map<int, uint256> MapCheckpoints;
-
-struct CCheckpointData {
-    MapCheckpoints mapCheckpoints;
-    int64_t nTimeLastCheckpoint;
-    int64_t nTransactionsLastCheckpoint;
-    double fTransactionsPerDay;
-};
 
 //! Return conservative estimate of total number of blocks, 0 if unknown
 int GetTotalBlocksEstimate(const CCheckpointData& data);