DELETE on system:tasks_cache can be executed by user without correct role

DELETE on system:tasks_cache can be performed by user without correct RBAC.

This means that any user can cancel any scheduled/running tasks.

For example, active ADVISOR sessions can be cancelled by any user.

Steps to repro:

1. Create a user without any roles assigned to it.

2. As the created user, run the statement below:

DELETE FROM system:tasks_cache;

The statement successfully executes which is incorrect. The user should have query_system_catalog role to perform the DELETE statement.