refactor(ap-change): remove unused payload from EnableStatement tracking base

[conomist]

Remove unused StatementIdx payload from ApTrackingBase::EnableStatement.
Replace EnableStatement(StatementIdx) with unit variant EnableStatement.
Drop obsolete #[expect(dead_code)] attribute that is no longer needed.

[chatgpt-codex-connector]

Codex usage limits have been reached for code reviews. Please check with the admins of this repo to increase the limits by adding credits.
Credits must be used to enable repository wide code reviews.

[reviewable-StarkWare]

This change is 

[orizi]

@orizi made 1 comment.
Reviewable status: 0 of 1 files reviewed, 1 unresolved discussion (waiting on conomist).

---

crates/cairo-lang-sierra-ap-change/src/compute.rs line 37 at r1 (raw file):

enum ApTrackingBase {
    FunctionStart(FunctionId),
    EnableStatement,

there on purpose. close PR.