Consider not enabling RBF by default

I know I know 🤣🤣 we just merged this.

But our timing for this PR (the one that made RBF signalling by default) was in a way quite late to the game. Bitcoin Core 0.28 now ships with full transaction replacement regardless of the RBF flag. This on its own doesn't really change anything for us, but after speaking with Murch on the Optech live podcast, his take on the RBF signalling is that in time, signalling _for_ RBF will actually fingerprint your wallet (because only few libraries will do that by default).

This is not really a pressing issue, but it's good to get the conversation going early. Over time if all transactions can always be RBF-ed and the ratio of RBF-signalling transaction keeps going down, it would probably make sense to revert the default to _not_ signalling for RBF.

BTW does anyone know if there is an easy place to find data on this? Like the ratio of transactions that signal for RBF over a given period of time? I wonder what's the proportion of tx in 2024 that do signal for it.