Remove suite body tracking from SemanticModel (#5848)

## Summary

The `SemanticModel` currently stores the "body" of a given `Suite`,
along with the current statement index. This is used to support "next
sibling" queries, but we only use this in exactly one place -- the rule
that simplifies constructs like this to `any` or `all`:

```python
for x in y:
    if x == 0:
        return True
return False
```

Instead of tracking the state, we can just do a (slightly more
expensive) traversal, by finding the node within its parent and
returning the next node in the body.

Note that we'll only have to do this extremely rarely -- namely, for
functions that contain something like:

```python
for x in y:
    if x == 0:
        return True
```

crates/ruff_python_semantic/src/model.rs

@@ -108,10 +108,6 @@ pub struct SemanticModel<'a> {
     /// by way of the `global x` statement.
     rebinding_scopes: HashMap<BindingId, Vec<ScopeId>, BuildNoHashHasher<BindingId>>,
 
-    /// Body iteration; used to peek at siblings.
-    pub body: &'a [Stmt],
-    pub body_index: usize,
-
     /// Flags for the semantic model.
     pub flags: SemanticModelFlags,
 
@@ -137,8 +133,6 @@ impl<'a> SemanticModel<'a> {
             shadowed_bindings: IntMap::default(),
             delayed_annotations: IntMap::default(),
             rebinding_scopes: IntMap::default(),
-            body: &[],
-            body_index: 0,
             flags: SemanticModelFlags::new(path),
             handled_exceptions: Vec::default(),
         }
@@ -757,11 +751,6 @@ impl<'a> SemanticModel<'a> {
         self.exprs.iter().rev().skip(1)
     }
 
-    /// Return the `Stmt` that immediately follows the current `Stmt`, if any.
-    pub fn sibling_stmt(&self) -> Option<&'a Stmt> {
-        self.body.get(self.body_index + 1)
-    }
-
     /// Returns a reference to the global scope
     pub fn global_scope(&self) -> &Scope<'a> {
         self.scopes.global()