tr: break Tr API in a couple ways

We fix the return value of Tr::tap_tree to return a Option<&T> instead
of an &Option<T>; we already do this in Descriptor::tap_tree, which is
likely to be more commonly called ... and both methods are pretty
obscure.

Also remove the iter_scripts method in favor of leaves. We did this
rename in the previous PR. However, that PR broke its API anyway by
making it yield an opaque struct rather than a tuple. Better to just do
all the breakage at once.

Maaybe we should backport the rename to 12.x as a pure rename, so that
people will update their code and get nicer error messages.

Author: apoelstra

src/descriptor/mod.rs

@@ -256,7 +256,7 @@ impl<Pk: MiniscriptKey> Descriptor<Pk> {
     /// returned value.
     pub fn tap_tree(&self) -> Option<&TapTree<Pk>> {
         if let Descriptor::Tr(ref tr) = self {
-            tr.tap_tree().as_ref()
+            tr.tap_tree()
         } else {
             None
         }
@@ -268,7 +268,7 @@ impl<Pk: MiniscriptKey> Descriptor<Pk> {
     /// Taproot descriptor containing only a keyspend, returns an empty iterator.
     pub fn tap_tree_iter(&self) -> tr::TapTreeIter<Pk> {
         if let Descriptor::Tr(ref tr) = self {
-            if let Some(ref tree) = tr.tap_tree() {
+            if let Some(tree) = tr.tap_tree() {
                 return tree.leaves();
             }
         }
@@ -988,7 +988,7 @@ impl<Pk: FromStrKey> FromStr for Descriptor<Pk> {
             // FIXME preserve weird/broken behavior from 12.x.
             // See https://github.com/rust-bitcoin/rust-miniscript/issues/734
             ret.sanity_check()?;
-            for item in inner.iter_scripts() {
+            for item in inner.leaves() {
                 item.miniscript()
                     .ext_check(&crate::miniscript::analyzable::ExtParams::sane())?;
             }

src/descriptor/tr/mod.rs

@@ -105,16 +105,7 @@ impl<Pk: MiniscriptKey> Tr<Pk> {
     pub fn internal_key(&self) -> &Pk { &self.internal_key }
 
     /// Obtain the [`TapTree`] of the [`Tr`] descriptor
-    pub fn tap_tree(&self) -> &Option<TapTree<Pk>> { &self.tree }
-
-    /// Obtain the [`TapTree`] of the [`Tr`] descriptor
-    #[deprecated(since = "11.0.0", note = "use tap_tree instead")]
-    pub fn taptree(&self) -> &Option<TapTree<Pk>> { self.tap_tree() }
-
-    /// Iterate over all scripts in merkle tree. If there is no script path, the iterator
-    /// yields [`None`]
-    #[deprecated(since = "TBD", note = "use `leaves` instead")]
-    pub fn iter_scripts(&self) -> TapTreeIter<Pk> { self.leaves() }
+    pub fn tap_tree(&self) -> Option<&TapTree<Pk>> { self.tree.as_ref() }
 
     /// Iterates over all the leaves of the tree in depth-first preorder.
     ///