Fix governance tutorial contract (#3948)

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>
Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>

docs/modules/ROOT/pages/governance.adoc

@@ -145,11 +145,11 @@ We can optionally set a proposal threshold as well. This restricts proposal crea
 // SPDX-License-Identifier: MIT
 pragma solidity ^0.8.2;
 
-import "./governance/Governor.sol";
-import "./governance/compatibility/GovernorCompatibilityBravo.sol";
-import "./governance/extensions/GovernorVotes.sol";
-import "./governance/extensions/GovernorVotesQuorumFraction.sol";
-import "./governance/extensions/GovernorTimelockControl.sol";
+import "@openzeppelin/contracts/governance/Governor.sol";
+import "@openzeppelin/contracts/governance/compatibility/GovernorCompatibilityBravo.sol";
+import "@openzeppelin/contracts/governance/extensions/GovernorVotes.sol";
+import "@openzeppelin/contracts/governance/extensions/GovernorVotesQuorumFraction.sol";
+import "@openzeppelin/contracts/governance/extensions/GovernorTimelockControl.sol";
 
 contract MyGovernor is Governor, GovernorCompatibilityBravo, GovernorVotes, GovernorVotesQuorumFraction, GovernorTimelockControl {
     constructor(IVotes _token, TimelockController _timelock)
@@ -173,24 +173,6 @@ contract MyGovernor is Governor, GovernorCompatibilityBravo, GovernorVotes, Gove
 
     // The functions below are overrides required by Solidity.
 
-    function quorum(uint256 blockNumber)
-        public
-        view
-        override(IGovernor, GovernorVotesQuorumFraction)
-        returns (uint256)
-    {
-        return super.quorum(blockNumber);
-    }
-
-    function getVotes(address account, uint256 blockNumber)
-        public
-        view
-        override(IGovernor, GovernorVotes)
-        returns (uint256)
-    {
-        return super.getVotes(account, blockNumber);
-    }
-
     function state(uint256 proposalId)
         public
         view