Remove GetTotalBlocksEstimate and checkpoint tests that test nothing.

GetTotalBlocksEstimate is no longer used and it was the only thing
 the checkpoint tests were testing.

Since checkpoints are on their way out it makes more sense to remove
 the test file than to cook up a new pointless test.

Github-Pull: #9053
Rebased-From: 2082b5574cec783f4ff99941492d92e05680b293

src/checkpoints.h

@@ -19,9 +19,6 @@ struct CCheckpointData;
 namespace Checkpoints
 {
 
-//! Return conservative estimate of total number of blocks, 0 if unknown
-int GetTotalBlocksEstimate(const CCheckpointData& data);
-
 //! Returns last CBlockIndex* in mapBlockIndex that is a checkpoint
 CBlockIndex* GetLastCheckpoint(const CCheckpointData& data);