Remove unused imports in example/tutorial macOS code

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer-rs/-/merge_requests/1512>

examples/src/examples-common.rs

@@ -29,7 +29,7 @@ where
         delegate,
     };
     use objc::{
-        class, msg_send,
+        msg_send,
         runtime::{Object, Sel},
         sel, sel_impl,
     };

tutorials/src/tutorials-common.rs

@@ -29,7 +29,7 @@ where
         delegate,
     };
     use objc::{
-        class, msg_send,
+        msg_send,
         runtime::{Object, Sel},
         sel, sel_impl,
     };