Remove redundant SignedTransaction::Signature

[emhane]

Since we can remove the op feature gated signature logic from reth-primitives, the signature AT is redundant

Ref #12184

[klkvr]

btw wondering which parts of the sdk actually need the fn signature() -> &Signature? wouldn't it be sufficient to just have something like trait Transaction { fn recover_signed(&self) -> Option<Address> }? that way the abstraction does not require each transaction to carry a concrete signature

[mattsse]

right, perhaps we can get around it like this, I think the only place we need to interact with the sig directly is win rpc, and this likely goes away and can be abstracted.

so we can proceed with this pr and should consider removing the sig fn if possible