ref(issues): removes custom views flag registration (#95694)

Removes `organizations:issue-stream-custom-views` from registration
after fully deprecating it:
- #95628
- getsentry/sentry-options-automator#4510

Author: cvxluo

src/sentry/features/temporary.py

@@ -161,8 +161,6 @@ def register_temporary_features(manager: FeatureManager):
     manager.add("organizations:issue-search-allow-postgres-only-search", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=False)
     # Whether to make a side/parallel query against events -> group_attributes when searching issues
     manager.add("organizations:issue-search-group-attributes-side-query", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=False)
-    # Enable custom views features in the issue stream
-    manager.add("organizations:issue-stream-custom-views", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
     # Enable issue stream performance improvements
     manager.add("organizations:issue-search-snuba", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=False)
     # Enable the new issue category mapping