Move UUPSUpgradeable to proxy/utils

(cherry picked from commit b9125001f0a1c44d596ca3a47536f1a467e3a29d)

contracts/mocks/UUPS/TestInProd.sol

@@ -3,7 +3,7 @@
 pragma solidity ^0.8.0;
 
 import "../CountersImpl.sol";
-import "../../proxy/UUPS/UUPSUpgradeable.sol";
+import "../../proxy/utils/UUPSUpgradeable.sol";
 
 contract UUPSUpgradeableMock is CountersImpl, UUPSUpgradeable {
     // Not having any checks in this function is dangerous! Do not do this outside tests!

contracts/proxy/ERC1967/ERC1967Upgrade.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.8.3;
+pragma solidity ^0.8.2;
 
 import "./ERC1967Storage.sol";
 

contracts/proxy/utils/Initializable.sol

@@ -3,8 +3,6 @@
 // solhint-disable-next-line compiler-version
 pragma solidity ^0.8.0;
 
-import "../../utils/Address.sol";
-
 /**
  * @dev This is a base contract to aid in writing upgradeable contracts, or any kind of contract that will be deployed
  * behind a proxy. Since a proxied contract can't have a constructor, it's common to move constructor logic to an