Remove residual SPM (SQL Plan Baseline) code

[footka]

Background

The core functionality of SQL Plan Management (SPM / SQL Plan Baseline) has been removed from seekdb: the DBMS_SPM package and Baseline lifecycle implementation have been deleted, Plan Baseline/SPM internal tables are marked as abandoned, and the Plan Cache loading Baseline implementation has been commented out. However, residual code remains, including system variables, empty manager pointers, DBMS_XPLAN display entry points, error codes/enums, comments, and orphaned result files.

Branch

master

Current State Quantification

• Approximately 40 source files contain SPM/SQL Plan Baseline related names or fields.
• System variables optimizer_use_sql_plan_baselines and optimizer_capture_sql_plan_baselines can still be set, but have no actual business logic reading them.
• ObPlanBaselineMgr only contains forward declarations and nullptr members; no implementation or initialization found.
• Two SPM mysqltests only have .result files remaining; their corresponding .test files have been deleted.

Scope of Work

1. Delete optimizer_use_sql_plan_baselines, optimizer_capture_sql_plan_baselines, and the generated system variable and Session Cache code.
2. Delete forward declarations of ObPlanBaselineMgr and residual empty pointers in Tenant Module/Module Provider/Observer.
3. Delete placeholder definitions for abandoned Plan Baseline/SPM internal tables, related schema declarations, and invalid display fields.
4. Delete the fully commented-out Baseline loading code in Plan Cache, along with unused enums like WAY_PLAN_BASELINE and PLAN_BASELINE_HANDLE.
5. Delete the DBMS_XPLAN.DISPLAY_SQL_PLAN_BASELINE interface, package declaration/body, and its access to the abandoned Baseline virtual tables.
6. Delete orphaned files spm_expr.result, spm_new_plan_not_ok.result, and other pure SPM comment/test residues.
7. Handle OB_SQL_RETRY_SPM: This error code is currently still used for EXPLAIN/Outline plan replay retries. It needs to be renamed with a new name reflecting Outline semantics while preserving the original retry behavior. The call chain cannot be directly deleted.

Boundaries

• Outline functionality must be preserved. CREATE/ALTER/DROP OUTLINE, Outline Schema/DDL, Plan Cache Outline status, optimizer Hint application, concurrency throttling, and related tests are not within the deletion scope of this task.
• Evolution/sampling logic reused in adaptive Plan Cache/Plan Expiration will be evaluated based on actual functionality; only invalid SPM semantics and dead code will be cleaned.

Acceptance Criteria

• The master branch compiles successfully, and Outline and Plan Cache related regression tests pass.
• The following searches yield no valid SPM residues: ObPlanBaseline, DBMS_SPM, SQL_PLAN_BASELINE, PLAN_BASELINE_HANDLE, WAY_PLAN_BASELINE, optimizer_use_sql_plan_baselines, optimizer_capture_sql_plan_baselines, OB_SQL_RETRY_SPM, __all_*plan_baseline, spm_*.
• Outline SQL creation, modification, deletion, and query plan application chains remain functional.
• DBMS_XPLAN no longer exposes SQL Plan Baseline display entry points that lack backend support.