Break testnet difficulty reset out of never matching condition.

Testnet resets difficulty if after 2 minutes no block has been found. However, this feature was implemented with the condition to only trigger on blocks where no retargeting is done. Since the introduction of DigiShield, we retarget at every block, making this condition never to be matched. This commit removes that condition.

***WARNING: THIS COMMIT HARDFORKS THE DOGECOIN TESTNET!***

The main network is not affected by this change.