Revert SQL function optimization

What does this MR do and why?

This change removes the previously created SQL functions for the primary key lookup optimization. The optimization didn't work out 100% and to fix it we would need to patch AR. I think implementing a solution that works for all cases is too expensive and dangerous to implement: !135196 (comment 1673038005)

Up:

main: == [advisory_lock_connection] object_id: 182760, pg_backend_pid: 1053275
main: == 20231219093121 DropUnusedSqlFunctions: migrating ===========================
main: -- execute("DROP FUNCTION IF EXISTS find_users_by_id")
main:    -> 0.0090s
main: -- execute("DROP FUNCTION IF EXISTS find_namespaces_by_id")
main:    -> 0.0005s
main: -- execute("DROP FUNCTION IF EXISTS find_projects_by_id")
main:    -> 0.0004s
main: == 20231219093121 DropUnusedSqlFunctions: migrated (0.0128s) ==================

main: == [advisory_lock_connection] object_id: 182760, pg_backend_pid: 1053275
ci: == [advisory_lock_connection] object_id: 182960, pg_backend_pid: 1053277
ci: == 20231219093121 DropUnusedSqlFunctions: migrating ===========================
ci: -- execute("DROP FUNCTION IF EXISTS find_users_by_id")
ci:    -> 0.0008s
ci: -- execute("DROP FUNCTION IF EXISTS find_namespaces_by_id")
ci:    -> 0.0003s
ci: -- execute("DROP FUNCTION IF EXISTS find_projects_by_id")
ci:    -> 0.0003s
ci: == 20231219093121 DropUnusedSqlFunctions: migrated (0.0085s) ==================

ci: == [advisory_lock_connection] object_id: 182960, pg_backend_pid: 1053277

Down:

ci: == [advisory_lock_connection] object_id: 182420, pg_backend_pid: 1058417
ci: == 20231219093121 DropUnusedSqlFunctions: reverting ===========================
ci: -- execute("CREATE OR REPLACE FUNCTION find_users_by_id(users_id bigint)\nRETURNS users AS $$\nBEGIN\n  return (SELECT users FROM users WHERE id = users_id LIMIT 1);\nEND;\n$$ LANGUAGE plpgsql STABLE PARALLEL SAFE COST 1;\n")
ci:    -> 0.0109s
ci: -- execute("CREATE OR REPLACE FUNCTION find_namespaces_by_id(namespaces_id bigint)\nRETURNS namespaces AS $$\nBEGIN\n  return (SELECT namespaces FROM namespaces WHERE id = namespaces_id LIMIT 1);\nEND;\n$$ LANGUAGE plpgsql STABLE PARALLEL SAFE COST 1;\n")
ci:    -> 0.0005s
ci: -- execute("CREATE OR REPLACE FUNCTION find_projects_by_id(projects_id bigint)\nRETURNS projects AS $$\nBEGIN\n  return (SELECT projects FROM projects WHERE id = projects_id LIMIT 1);\nEND;\n$$ LANGUAGE plpgsql STABLE PARALLEL SAFE COST 1;\n")
ci:    -> 0.0004s
ci: == 20231219093121 DropUnusedSqlFunctions: reverted (0.0194s) ==================

ci: == [advisory_lock_connection] object_id: 182420, pg_backend_pid: 1058417


main: == [advisory_lock_connection] object_id: 182420, pg_backend_pid: 1058797
main: == 20231219093121 DropUnusedSqlFunctions: reverting ===========================
main: -- execute("CREATE OR REPLACE FUNCTION find_users_by_id(users_id bigint)\nRETURNS users AS $$\nBEGIN\n  return (SELECT users FROM users WHERE id = users_id LIMIT 1);\nEND;\n$$ LANGUAGE plpgsql STABLE PARALLEL SAFE COST 1;\n")
main:    -> 0.0107s
main: -- execute("CREATE OR REPLACE FUNCTION find_namespaces_by_id(namespaces_id bigint)\nRETURNS namespaces AS $$\nBEGIN\n  return (SELECT namespaces FROM namespaces WHERE id = namespaces_id LIMIT 1);\nEND;\n$$ LANGUAGE plpgsql STABLE PARALLEL SAFE COST 1;\n")
main:    -> 0.0006s
main: -- execute("CREATE OR REPLACE FUNCTION find_projects_by_id(projects_id bigint)\nRETURNS projects AS $$\nBEGIN\n  return (SELECT projects FROM projects WHERE id = projects_id LIMIT 1);\nEND;\n$$ LANGUAGE plpgsql STABLE PARALLEL SAFE COST 1;\n")
main:    -> 0.0005s
main: == 20231219093121 DropUnusedSqlFunctions: reverted (0.0152s) ==================

main: == [advisory_lock_connection] object_id: 182420, pg_backend_pid: 1058797