Remove proxyOwner method from proxy contract

[patitonar]

Closes #195

[akolotov]

We got the following comment during the security audit:

line 10 (address private _upgradeabilityOwner;), why do you use private visibility modifier instead of internal? (edited)

Do you think it make sense to make this one-line-change under this PR?

[patitonar]

line 10 (address private _upgradeabilityOwner;), why do you use private visibility modifier instead of internal? (edited)
Do you think it make sense to make this one-line-change under this PR?

Sure, it is related. Added the change on this commit e73d2aa