style: drop stray blank lines left by the test-file splits

The `sed`-based extractions in the preceding three split commits each
left one extra blank line at the cut boundary, which `cargo fmt --all
--check` (a CI gate) rejects. Whitespace only — no code change.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/ely_browser_core/tests/splits.rs

@@ -263,4 +263,3 @@ fn detach_split_pane_refreshes_saved_split_title() -> Result<(), Box<dyn Error>>
     assert_eq!(layout.pane_count(), 2);
     Ok(())
 }
-