fix: remove duplicate Default derive in ProxyType

Removed duplicate Default trait in derive macro which was causing
conflicting implementations error (E0119).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: drewstone

runtime/testnet/src/lib.rs

@@ -1145,7 +1145,6 @@ parameter_types! {
 	Default,
 	Copy,
 	Clone,
-	Default,
 	Eq,
 	PartialEq,
 	Ord,