Ensures that the L2 contracts cannot be reinitialized by
making their storage value for `_initialze` match the value
that is hardcoded in the contract. Since the call to `initialize()`
never actually runs in the L2 genesis generation, we only have
contract over setting state. Trying to call `reinitialize` again
with the same value will cause it to revert.

Also remove the unnecessary argument to the `L2ERC721Bridge`. This
was noticed by trail of bits during the audit. It adds extra assurance
that the `initialize` functions take no arguments on L2, meaning that
even if they could be reinitialized, nothing horrible could happen.
Note that this is very application specific and would result in nothing
horrible happening based on how the optimism contracts are designed.
We should stil not allow for contracts to be reinitialized.

In the far future, we will move towards removing the concept of
`initialize` completely by breaking storage layout migrations
into their own upgrade step.