Undo debugging change from 5be6abbf84

This was unintentionally committed, and caused Equihash verification of blocks
without parents to be skipped. This only affects the genesis block on the test
network, but also causes the "time verifyequihash" benchmark to incorrectly
appear instantaneous.

src/pow.cpp

@@ -96,10 +96,6 @@ unsigned int CalculateNextWorkRequired(uint32_t nBits, int64_t nLastBlockTime, i
 
 bool CheckEquihashSolution(const CBlockHeader *pblock, const CChainParams& params)
 {
-    // Don't validate genesis
-    if (pblock->hashPrevBlock.IsNull())
-        return true;
-
     unsigned int n = params.EquihashN();
     unsigned int k = params.EquihashK();