sim: Remove extraneous slice reference

Clippy suggests that the reference is unnecessary when making a
comparison.

Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/sim/src/image.rs b/sim/src/image.rs
index 3bdcc22..cfe20b5 100644
--- a/sim/src/image.rs
+++ b/sim/src/image.rs
@@ -1514,7 +1514,7 @@
                 true
             } else if v == 3 {
                 let expected = [erased_val; 16];
-                if &copy[24..] != expected {
+                if copy[24..] != expected {
                     warn!("\"magic\" mismatch at {:#x}", offset);
                     true
                 } else {