Remove rustfmt --recursive option

Summary:
D35234535 updated rustfmt, which no longer has `--recursive` option.

`rustfmt` [seems to](rust-lang/rustfmt#5018 (comment)) flip `--recursive` option with `--skip-children`.

Reviewed By: bobyangyf

Differential Revision: D35240294

fbshipit-source-id: bbcd4dc3556c0753c07f3cbe380553e6426d1527

test.py

@@ -118,7 +118,7 @@ def rustfmt(buck2_dir: Path, ci: bool) -> None:
     env["RUSTFMT"] = str(
         buck2_dir.parent.parent / "tools" / "third-party" / "rustfmt" / "rustfmt"
     )
-    output = run([cargo_fmt, "--", "--recursive"], capture_output=True, env=env).stdout
+    output = run([cargo_fmt, "--"], capture_output=True, env=env).stdout
     for line in output.splitlines():
         # The fbsource formatter spews out:
         #   Warning: the `merge_imports` option is deprecated. Use `imports_granularity=Crate` instead