fix(golang): remove runtime_metrics_enabled from OTLP_RUNTIME_METRICS scenario

DD_RUNTIME_METRICS_ENABLED=true (set by runtime_metrics_enabled=True) causes the
old StatsD runtime.go.* metrics to be emitted alongside the new OTel go.* metrics,
making test_dd_metrics_are_absent fail. The scenario tests OTel metrics as a
replacement for DD-proprietary ones, so the old DD runtime metrics must be off.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: anna-git

utils/_context/_scenarios/__init__.py

@@ -1321,7 +1321,6 @@ class _Scenarios:
             "OTEL_EXPORTER_OTLP_METRICS_HEADERS": "dd-protocol=otlp,dd-otlp-path=agent",
             "GOMEMLIMIT": "500MiB",
         },
-        runtime_metrics_enabled=True,
         include_opentelemetry=True,
         library_interface_timeout=20,
         doc="Test runtime metrics exported via OTLP with OTel semantic convention names",