Execute drop function failed if deployment reference it

deployment will run failed if relevant function has been dropped. so we should check if there are any deployments referred when drop the function.
known issue in #1509

The issue references a known problem from #1509. Start by examining the function drop logic in the codebase, likely in SQL execution or DDL handling modules. Look for existing deployment references and add a check to prevent dropping functions that are in use. Review #1509 for context and existing discussions.

Written by the indexing model from the issue text.