remove AlertGroup.is_restricted column #5264

Job	Run time
Lint database migrations	1m 22s
Lint entire project	1m 29s
Lint, test, and build frontend	1m 49s
mypy	1m 30s
Test technical documentation	24s
Backend Tests: MySQL + RabbitMQ (RBAC enabled: True)	2m 51s
Backend Tests: PostgreSQL + RabbitMQ (RBAC enabled: True)	2m 58s
Backend Tests: MySQL + RabbitMQ (RBAC enabled: False)	3m 7s
Backend Tests: PostgreSQL + RabbitMQ (RBAC enabled: False)	3m 19s
Backend Tests: SQLite + Redis (RBAC enabled: True)	2m 47s
Backend Tests: SQLite + Redis (RBAC enabled: False)	3m 4s
Helm Chart Unit Tests	21s
Unit tests - PagerDuty Migrator	21s
End to end tests / Grafana: 10.0.2	16m 40s
	42m 2s

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