doc: fix broken link and stranded doccomment

(The stranded doccomment was associated with commented-out code, but
rustdoc was applying it to the nearest non-commented-out item. Just
delete all the commented-out stuff since we're not going to reenable
it in 12.x.)

Author: apoelstra

src/descriptor/mod.rs

@@ -648,7 +648,7 @@ impl Descriptor<DescriptorPublicKey> {
     /// See [`at_derivation_index`] and `[derived_descriptor`] for more documentation.
     ///
     /// [`at_derivation_index`]: Self::at_derivation_index
-    /// [`derived_descriptor`]: crate::DerivedDescriptor::derived_descriptor
+    /// [`derived_descriptor`]: crate::Descriptor::derived_descriptor
     ///
     /// # Errors
     ///

src/lib.rs

@@ -401,16 +401,6 @@ where
         T: Translator<P, Q, E>;
 }
 
-/// Either a key or keyhash, but both contain Pk
-// pub struct ForEach<'a, Pk: MiniscriptKey>(&'a Pk);
-
-// impl<'a, Pk: MiniscriptKey<Hash = Pk>> ForEach<'a, Pk> {
-//     /// Convenience method to avoid distinguishing between keys and hashes when these are the same type
-//     pub fn as_key(&self) -> &'a Pk {
-//         self.0
-//     }
-// }
-
 /// Trait describing the ability to iterate over every key
 pub trait ForEachKey<Pk: MiniscriptKey> {
     /// Run a predicate on every key in the descriptor, returning whether