Remove wrong TODO comment in build_fee_bump

The proposed solution is bad for privacy as well.
Let's call the initial change output, which is normally shrink when you
fee bump, change#1, and the extra output aforementioned change#2 (as,
in this case, it's going to be a change output as well). If you add change#2
you might not revel change#1, but you're still revealing change#2.
You're not improving your privacy, and you're wasting money in fees.

src/wallet/mod.rs

@@ -899,8 +899,6 @@ where
     /// # Ok::<(), bdk::Error>(())
     /// ```
     // TODO: support for merging multiple transactions while bumping the fees
-    // TODO: option to force addition of an extra output? seems bad for privacy to update the
-    // change
     pub fn build_fee_bump(
         &self,
         txid: Txid,