Use only 1 initializable instead of two different initializable
imports. Using contracts with the same name will break hardhat.

The two different initializable imports were:

```solidity
import { Initializable } from "@openzeppelin/contracts-upgradeable/proxy/utils/Initializable.sol";
```

```solidity
import { Initializable } from "@openzeppelin/contracts/proxy/utils/Initializable.sol";
```

This standardizes on not using `contracts-upgradeable`.