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_parser/src/snapshots/ruff_python_parser__parser__tests__try.snap

@@ -243,6 +243,7 @@ expression: parse_ast
             ],
             orelse: [],
             finalbody: [],
+            is_star: false,
         },
     ),
 ]

crates/ruff_python_parser/src/snapshots/ruff_python_parser__parser__tests__try_star.snap

@@ -3,8 +3,8 @@ source: crates/ruff_python_parser/src/parser.rs
 expression: parse_ast
 ---
 [
-    TryStar(
-        StmtTryStar {
+    Try(
+        StmtTry {
             range: 0..260,
             body: [
                 Raise(
@@ -436,6 +436,7 @@ expression: parse_ast
             ],
             orelse: [],
             finalbody: [],
+            is_star: true,
         },
     ),
 ]