Revert merge of pull #4845

It breaks the new mingw tests!

See

- https://travis-ci.org/bitcoin/bitcoin/jobs/36845581
- https://travis-ci.org/bitcoin/bitcoin/jobs/36845582

This reverts commit 4705902777, 5e2e7fcb99, a25fd6be13.

src/checkpoints.cpp

@@ -88,8 +88,6 @@ namespace Checkpoints {
             return dataTestnet;
         else if (Params().NetworkID() == CBaseChainParams::MAIN)
             return data;
-        else if (Params().NetworkID() == CBaseChainParams::UNITTEST) // UnitTest share the same checkpoints as MAIN
-            return data;
         else
             return dataRegtest;
     }