fix: Apply linter result

Author: seedspirit

src/ai/backend/common/clients/valkey_client/valkey_stat/client.py

@@ -24,7 +24,6 @@
 from ai.backend.common.exception import BackendAIError
 from ai.backend.common.json import dump_json_str, load_json
 from ai.backend.common.metrics.metric import DomainType, LayerType
-from ai.backend.common.metrics.types import MetricValue
 from ai.backend.common.resilience import (
     BackoffStrategy,
     MetricArgs,