fix: remove legacy bnf

tests/hello_rpg.rs

@@ -1,7 +1,7 @@
 //! Integration tests for the compiler binary against the Hello World program.
 //!
 //! These tests exercise the full compilation pipeline:
-//!   hello.rpg → BNF validation → AST lowering → LLVM codegen → native binary
+//!   hello.rpg → recursive-descent parser → AST lowering → LLVM codegen → native binary
 
 use std::process::Command;
 
@@ -71,7 +71,7 @@ fn hello_rpg_produces_output_file() {
 }
 
 /// The compiler must print the file name to stderr with an "ok:" prefix when
-/// BNF validation succeeds.
+/// compilation succeeds.
 #[test]
 fn hello_rpg_reports_ok_on_stderr() {
     let out_path = std::env::temp_dir().join("hello_rpg_reports_ok.out");
@@ -121,33 +121,6 @@ fn hello_rpg_emit_ir() {
     );
 }
 
-/// `--emit-tree` must print the BNF parse tree to stdout and exit 0.
-///
-/// The tree must mention `program` (the top-level grammar rule).
-#[test]
-fn hello_rpg_emit_tree() {
-    let out = run(&["--emit-tree", HELLO_RPG]);
-
-    assert!(
-        out.status.success(),
-        "expected exit 0 with --emit-tree\nstderr: {}",
-        String::from_utf8_lossy(&out.stderr),
-    );
-
-    let tree = String::from_utf8_lossy(&out.stdout);
-
-    assert!(
-        !tree.trim().is_empty(),
-        "--emit-tree output is empty — expected a parse tree",
-    );
-
-    assert!(
-        tree.contains("program"),
-        "--emit-tree output should reference the <program> rule\n{}",
-        &tree[..tree.len().min(1000)],
-    );
-}
-
 /// `--no-link` should produce a `.o` object file and exit 0.
 #[test]
 fn hello_rpg_no_link_produces_object() {