Move `VestingWallet`'s beneficiary zero address check to `Ownable`

[ernestognw]

Description

Currently, VestingWallet makes a check to validate that the owner is not the zero address. However, we consider this check should be performed in the Ownable contract instead.

maybe not in the PR, but we should remove that check here and move it to Ownable's constructor

Originally posted by @Amxx in #4508 (comment)