Remove 'static requirement on run

There's no need to force the static on the users, given that internally
some backends were not using static in the first place.

Co-authored-by: daxpedda <daxpedda@gmail.com>

src/platform_impl/macos/event_loop.rs

@@ -195,7 +195,7 @@ impl<T> EventLoop<T> {
 
     pub fn run<F>(mut self, callback: F) -> Result<(), RunLoopError>
     where
-        F: 'static + FnMut(Event<T>, &RootWindowTarget<T>, &mut ControlFlow),
+        F: FnMut(Event<T>, &RootWindowTarget<T>, &mut ControlFlow),
     {
         self.run_ondemand(callback)
     }