sim: Remove elided lifetime

This lifetime can be inferred by the compiler, so remove the explicit
one.  This makes the code a little easier to read.

Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/sim/src/image.rs b/sim/src/image.rs
index c420645..1fdb1f0 100644
--- a/sim/src/image.rs
+++ b/sim/src/image.rs
@@ -1704,7 +1704,7 @@
 
 /// Return a read-only view into the raw bytes of this object
 trait AsRaw : Sized {
-    fn as_raw<'a>(&'a self) -> &'a [u8] {
+    fn as_raw(&self) -> &[u8] {
         unsafe { slice::from_raw_parts(self as *const _ as *const u8,
                                        mem::size_of::<Self>()) }
     }