Suppress unused_imports that are used

Summary:
## This diff
This is actually used, but I guess the macro stuff confuses the linter.

## This stack
We have some annoying unused deps warnings all over Citadel.

Some can be cleaned up, some are actually used and some are due to the fact that we moved code without moving the tests too.

Reviewed By: anaypaul

Differential Revision: D91927999

fbshipit-source-id: f39747397a478a0fe4d955d714a4f70230f66dce

Author: Kosie van der Merwe

td_util/src/supertd_events_logger.rs

@@ -98,7 +98,9 @@ mod linux {
         compile_error!("duplicate `event` field in `scuba!` macro");
     };
     ( @SET_FIELD ( $builder:ident, data, $value:expr ) ) => {{
+        #[allow(unused_imports)]
         use $crate::supertd_events::serde_json::json;
+
         match $crate::supertd_events::serde_json::to_string(&$value) {
             Ok(json) => {
                 $builder.set_data(json);