fix: delete some dead code using vulture (#20999)

Signed-off-by: yihong0618 <zouzou0208@gmail.com>

api/core/workflow/nodes/event/event.py

 from core.model_runtime.entities.llm_entities import LLMUsage
 from core.rag.entities.citation_metadata import RetrievalSourceMetadata
 from core.workflow.entities.node_entities import NodeRunResult
-from core.workflow.entities.workflow_node_execution import WorkflowNodeExecutionStatus
 
 
 class RunCompletedEvent(BaseModel):
     error: str = Field(..., description="error")
     retry_index: int = Field(..., description="Retry attempt number")
     start_at: datetime = Field(..., description="Retry start time")
-
-
-class SingleStepRetryEvent(NodeRunResult):
-    """Single step retry event"""
-
-    status: WorkflowNodeExecutionStatus = WorkflowNodeExecutionStatus.RETRY
-
-    elapsed_time: float = Field(..., description="elapsed time")

api/factories/variable_factory.py

 from core.workflow.constants import CONVERSATION_VARIABLE_NODE_ID, ENVIRONMENT_VARIABLE_NODE_ID
 
 
-class InvalidSelectorError(ValueError):
-    pass
-
-
 class UnsupportedSegmentTypeError(Exception):
     pass
 

api/services/errors/__init__.py

     app_model_config,
     audio,
     base,
-    completion,
     conversation,
     dataset,
     document,
     "app_model_config",
     "audio",
     "base",
-    "completion",
     "conversation",
     "dataset",
     "document",

api/services/errors/account.py

 
 class RoleAlreadyAssignedError(BaseServiceError):
     pass
-
-
-class RateLimitExceededError(BaseServiceError):
-    pass

api/services/errors/completion.py

-from services.errors.base import BaseServiceError
-
-
-class CompletionStoppedError(BaseServiceError):
-    pass