Fix CPP retirement pension integration

- Add cpp_retirement_pension to household benefits aggregation
- Remove unnecessary self-referential adds declaration

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: MaxGhenis

policyengine_canada/variables/gov/benefits.py

@@ -11,6 +11,7 @@ class benefits(Variable):
         "child_benefit",
         "child_disability_benefit",
         "canada_workers_benefit",
+        "cpp_retirement_pension",
         "dental_benefit",
         "oas_net",
         # Ontario programs.

policyengine_canada/variables/gov/cra/benefits/cpp/cpp_retirement_pension.py

@@ -8,7 +8,6 @@ class cpp_retirement_pension(Variable):
     definition_period = YEAR
     unit = CAD
     documentation = "Annual CPP retirement pension amount"
-    adds = ["cpp_retirement_pension"]
 
     def formula(person, period, parameters):
         p = parameters(period).gov.cra.benefits.cpp.retirement