UnitTestParams: don't solve() the genesis block for unit tests

It won't really solve it anyway, because the difficulty check is
disabled.

core/src/main/java/org/bitcoinj/params/UnitTestParams.java

@@ -76,7 +76,6 @@ public class UnitTestParams extends BitcoinNetworkParams {
                 genesisBlock = Block.createGenesis();
                 genesisBlock.setDifficultyTarget(Block.EASIEST_DIFFICULTY_TARGET);
                 genesisBlock.setTime(TimeUtils.currentTime());
-                genesisBlock.solve();
             }
         }
         return genesisBlock;