Obey training.planner.log_plan flag on if to log sharding plan (#3244)

Summary:
Pull Request resolved: #3244

## Why
Sharding plan can be verbose and we used to control if to log it via training.planner.log_plan, which creates NoopEmbeddingStats when is False and valid stats otherwise:
https://www.internalfb.com/code/fbsource/[375d786e20a4]/fbcode/apf/rec/distributed/parallel.py?lines=872-882

D74557713 adds a new logging on the raw sharding plan without following this flag. This diffs guards it with the flag.

## What
Only log the raw sharding plan when there is valid stats (i.e. not NoopEmbeddingStats).

Reviewed By: ge0405

Differential Revision: D79271421

fbshipit-source-id: bc16a5bf4349780a9f316a5f6ccc65489e77672a

Author: silverlakeli

torchrec/distributed/planner/planners.py

@@ -32,7 +32,7 @@
     GridSearchProposer,
     UniformProposer,
 )
-from torchrec.distributed.planner.stats import EmbeddingStats
+from torchrec.distributed.planner.stats import EmbeddingStats, NoopEmbeddingStats
 from torchrec.distributed.planner.storage_reservations import (
     HeuristicalStorageReservation,
 )
@@ -513,7 +513,10 @@ def plan(
             sharding_plan = to_sharding_plan(best_plan, self._topology)
 
             end_time = perf_counter()
+            shall_log_sharding_plan = False
             for stats in self._stats:
+                if not isinstance(stats, NoopEmbeddingStats):
+                    shall_log_sharding_plan = True
                 stats.log(
                     sharding_plan=sharding_plan,
                     topology=self._topology,
@@ -528,7 +531,8 @@ def plan(
                     sharders=sharders,
                     debug=self._debug,
                 )
-            logger.info(f"Found sharding plan {sharding_plan}")
+            if shall_log_sharding_plan:
+                logger.info(f"Found sharding plan {sharding_plan}")
             return sharding_plan
         else:
             global_storage_capacity = reduce(