sim: Simplify printing blank line

Per clippy, `println!()` should be used instead of `println!("")`.

Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/sim/src/image.rs b/sim/src/image.rs
index 8251a6a..3bdcc22 100644
--- a/sim/src/image.rs
+++ b/sim/src/image.rs
@@ -1239,7 +1239,7 @@
         println!("    {:3}: 0x{:08x}, 0x{:08x}",
                  sector.num, sector.base, sector.size);
     }
-    println!("");
+    println!();
 }
 
 /// Install a "program" into the given image.  This fakes the image header, or at least all of the