Revert "Update packages/bigframes/bigframes/session/metrics.py"

This reverts commit a46ce69.

Author: shuoweil

packages/bigframes/bigframes/session/metrics.py

@@ -248,7 +248,6 @@ def on_event(self, event: Any):
                 self.execution_count += 1
                 bytes_processed = event.result.total_bytes_processed or 0
                 self.bytes_processed += bytes_processed
-                self.bytes_processed += bytes_processed
 
                 metadata = JobMetadata(
                     job_type="polars",