Duplicated owner's fields in EternalProxy

there are 2 methods:

```solidity
    function upgradeabilityOwner() public view returns (address) {
        return _upgradeabilityOwner;
    }
```
and 

```solidity
    function proxyOwner() public view returns (address) {
        return upgradeabilityOwner();
    }
```

I don't see any good reason to have those 2
