Remove empty TRACK_DIAGNOSTIC calls.

They have no apparent effect.

Author: nnethercote

compiler/rustc_errors/src/lib.rs

@@ -1304,14 +1304,10 @@ impl DiagCtxtInner {
             && !self.flags.can_emit_warnings
             && !diagnostic.is_force_warn()
         {
-            if diagnostic.has_future_breakage() {
-                (*TRACK_DIAGNOSTIC)(diagnostic, &mut |_| {});
-            }
             return None;
         }
 
         if matches!(diagnostic.level, Expect(_) | Allow) {
-            (*TRACK_DIAGNOSTIC)(diagnostic, &mut |_| {});
             return None;
         }