Decide whether PerformanceMonitor drops rules 21, 25 and 31, which PerformanceStudio removed #4537

Part of #4511, the sync of plan analysis changes from PerformanceStudio (PS) to PerformanceMonitor (PM).

PM still runs three rules that PS removed after the review of its rule set in erikdarlingdata/PerformanceStudio#215:

• Rule 21, CTE Multiple References (PlanAnalyzer.cs:269, with its detector at line 1272).
• Rule 25, Ineffective Parallelism (PlanAnalyzer.cs:325).
• Rule 31, Parallel Wait Bottleneck (PlanAnalyzer.cs:312).

erikdarlingdata/PerformanceStudio@aabbaa2 (erikdarlingdata/PerformanceStudio#266) removed rule 21. The reason in the PS code is that an actual plan's runtime stats show where the time went. So a warning based on a text pattern for CTE reuse is a guess.

erikdarlingdata/PerformanceStudio@28d4c74 removed rules 25 and 31. The reason in that commit is that these warnings guess at causes that the wait stats already show. PS shows a ratio of CPU to elapsed time in its runtime summary instead.

Decide whether PM removes these rules too. If PM removes rules 25 and 31, also remove their cases in BenefitScorer.cs (lines 51 and 52).

At 1899737f. dev has no later change to PerformanceMonitor.PlanAnalysis.