chore(contract): disable empty code blocks warnings

contracts/contracts/MACI.sol

@@ -9,7 +9,6 @@ import { AccQueue } from "./trees/AccQueue.sol";
 import { AccQueueQuinaryBlankSl } from "./trees/AccQueueQuinaryBlankSl.sol";
 import { IMACI } from "./interfaces/IMACI.sol";
 import { Params } from "./utilities/Params.sol";
-import { DomainObjs } from "./utilities/DomainObjs.sol";
 import { TopupCredit } from "./TopupCredit.sol";
 import { Utilities } from "./utilities/Utilities.sol";
 import { Ownable } from "@openzeppelin/contracts/access/Ownable.sol";

contracts/contracts/PollFactory.sol

@@ -20,6 +20,7 @@ contract PollFactory is Params, DomainObjs {
   error InvalidMaxValues();
 
   /// @notice The PollFactory constructor
+  // solhint-disable-next-line no-empty-blocks
   constructor() payable {}
 
   /// @notice Deploy a new Poll contract and AccQueue contract for messages.

contracts/contracts/VkRegistry.sol

@@ -31,6 +31,7 @@ contract VkRegistry is Ownable, SnarkCommon {
   error SubsidyVkNotSet();
 
   /// @notice Create a new instance of the VkRegistry contract
+  // solhint-disable-next-line no-empty-blocks
   constructor() payable {}
 
   /// @notice Check if the process verifying key is set

contracts/contracts/gatekeepers/FreeForAllSignUpGatekeeper.sol

@@ -8,10 +8,12 @@ import { SignUpGatekeeper } from "./SignUpGatekeeper.sol";
 /// @notice A SignUpGatekeeper which allows anyone to sign up.
 contract FreeForAllGatekeeper is SignUpGatekeeper {
   /// @notice Create a new instance of FreeForAllGatekeeper
+  // solhint-disable-next-line no-empty-blocks
   constructor() payable {}
 
   /// @notice setMaciInstance does nothing in this gatekeeper
   /// @param _maci The MACI contract
+  // solhint-disable-next-line no-empty-blocks
   function setMaciInstance(MACI _maci) public override {}
 
   /// @notice Registers the user without any restrictions.