Remove MQ tracing for postSyncBarriers

They go through the same enqueueMessage path which is already
traced. So we were double tracing them.

Test: Manual
Bug: 402524956
Bug: 403793333
Flag: android.os.perfetto_sdk_tracing_v2
Change-Id: Ie097615d489f05a8e838f8618fca2216d9665373