ref(dashboards): remove dashboards-categorical-bar-charts flag declaration (#109897)

Remove the `organizations:dashboards-categorical-bar-charts` flag
declaration from `temporary.py`.

The feature has been fully rolled out via flagpole. This PR removes the
backend flag declaration.

Companion PRs:
- Frontend (feature check removal):
#109896
- sentry-options-automator (flag definition removal):
getsentry/sentry-options-automator#6696

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

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: gggritso

src/sentry/features/temporary.py

@@ -76,8 +76,6 @@ def register_temporary_features(manager: FeatureManager) -> None:
     manager.add("organizations:daily-summary", OrganizationFeature, FeatureHandlerStrategy.INTERNAL, api_expose=False)
     # Enables read only dashboards
     manager.add("organizations:dashboards-basic", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True, default=True)
-    # Enable categorical bar charts for dashboards
-    manager.add("organizations:dashboards-categorical-bar-charts", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
     # Enables custom editable dashboards
     manager.add("organizations:dashboards-edit", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True, default=True)
     # Enables favourite and duplicate controls for prebuilt dashboards