use shorthand constraint syntax and formatting

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/utils/defer.rs

@@ -1,17 +1,11 @@
 #[macro_export]
 macro_rules! defer {
 	($body:block) => {
-		struct _Defer_<F>
+		struct _Defer_<F: FnMut()> {
-		where
-			F: FnMut(),
-		{
 			closure: F,
 		}
 
-		impl<F> Drop for _Defer_<F>
+		impl<F: FnMut()> Drop for _Defer_<F> {
-		where
-			F: FnMut(),
-		{
 			fn drop(&mut self) { (self.closure)(); }
 		}