Remove Stmt::TryStar (#6566)

## Summary

Instead, we set an `is_star` flag on `Stmt::Try`. This is similar to the
pattern we've migrated towards for `Stmt::For` (removing
`Stmt::AsyncFor`) and friends. While these are significant differences
for an interpreter, we tend to handle these cases identically or nearly
identically.

## Test Plan

`cargo test`

crates/ruff_python_ast/src/visitor.rs

@@ -266,20 +266,7 @@ pub fn walk_stmt<'a, V: Visitor<'a> + ?Sized>(visitor: &mut V, stmt: &'a Stmt) {
             handlers,
             orelse,
             finalbody,
-            range: _,
-        }) => {
-            visitor.visit_body(body);
-            for except_handler in handlers {
-                visitor.visit_except_handler(except_handler);
-            }
-            visitor.visit_body(orelse);
-            visitor.visit_body(finalbody);
-        }
-        Stmt::TryStar(ast::StmtTryStar {
-            body,
-            handlers,
-            orelse,
-            finalbody,
+            is_star: _,
             range: _,
         }) => {
             visitor.visit_body(body);