sim: Remove padding from ecdsa signatures

With support for unpadded ecdsa signatures in place, always generate
unpadded signatures within the sim.

Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/sim/src/tlv.rs b/sim/src/tlv.rs
index 4fbafd4..c8200e6 100644
--- a/sim/src/tlv.rs
+++ b/sim/src/tlv.rs
@@ -412,12 +412,7 @@
 
             result.write_u16::<LittleEndian>(TlvKinds::ECDSA256 as u16).unwrap();
 
-
-            // signature must be padded...
-            let mut signature = signature.as_ref().to_vec();
-            while signature.len() < 72 {
-                signature.push(0);
-            }
+            let signature = signature.as_ref().to_vec();
 
             result.write_u16::<LittleEndian>(signature.len() as u16).unwrap();
             result.extend_from_slice(signature.as_ref());