Remove debug prints that probably shouldn't have been merged

Also add a comment to the one place `eprintln!` is used to explain why
it's appropriate.

src/backend/winit.rs

@@ -113,7 +113,7 @@ impl WinitState {
             .get::<RefCell<OutputConfig>>()
             .unwrap()
             .borrow_mut();
-        if dbg!(config.mode.0) != dbg!((size.w, size.h)) {
+        if config.mode.0 != (size.w, size.h) {
             if !test_only {
                 config.mode = ((size.w, size.h), None);
             }