RemoveSystem.cs

using Unity.Entities;
using Unity.Jobs;
using Unity.Transforms;
using UnityEngine;
using Unity.Mathematics;
using Unity.Collections;

class RangeCheckSystem : JobComponentSystem
{
    EntityCommandBufferSystem barrier; // EntityCommandBufferSystemを用意
    EntityQuery query;

    protected override void OnCreate()
    {
        base.OnCreate();

        barrier = World.GetOrCreateSystem<EndSimulationEntityCommandBufferSystem>();
        query = GetEntityQuery(ComponentType.ReadOnly<Translation>());
    }

    protected override JobHandle OnUpdate(JobHandle inputDeps)
    {
        inputDeps = new RangeCheckJob
        {
            mousePosition = Camera.main.ScreenToWorldPoint(Input.mousePosition + Vector3.forward * 10),
            commandBuffer = barrier.CreateCommandBuffer().ToConcurrent(), // ToConcurrentを使用
        }.Schedule(this, inputDeps);

        barrier.AddJobHandleForProducer(inputDeps); // 終了時にはAddJobHandleForProducer

        return inputDeps;
    }


    [Unity.Burst.BurstCompile]
    struct RangeCheckJob : IJobForEachWithEntity<Translation>
    {
        public Vector3 mousePosition;
        [ReadOnly]
        public EntityCommandBuffer.Concurrent commandBuffer;   // 利用する側もConcurrent。何故かReadOnlyが必要
        public void Execute(Entity entity, int index, ref Translation position)
        {
            if( math.distance(position.Value, mousePosition) < 1)
            {
                commandBuffer.DestroyEntity(index, entity);
            }
        }
    }
}

Spawner.cs

using UnityEngine;
using Unity.Entities;
using Unity.Transforms;
using Unity.Collections;
using Unity.Mathematics;
using Random = Unity.Mathematics.Random;

public class GameController : MonoBehaviour
{
    [SerializeField] GameObject prefab;

    NativeArray<Entity> entities;

    const int count = 4000;

    void Awake()
    {
        entities = new NativeArray<Entity>(count, Allocator.Persistent, NativeArrayOptions.UninitializedMemory);

        var entity =  GameObjectConversionUtility.ConvertGameObjectHierarchy(prefab, World.Active);
        
        var entityManager = World.Active.EntityManager;
        entityManager.Instantiate(entity, entities);
        Random random = new Random(128);

        for (int i = 0; i < count; i++)
        {
            var pos = new float3(random.NextFloat(-10, 10), random.NextFloat(-10, 10), 0);
            entityManager.SetComponentData(entities[i], new Translation() { Value = pos });
        }

        World.Active.EntityManager.DestroyEntity(entity);
        entities.Dispose();
    }
}