revert(ecs): add validation checks to memory cpu combinations of FARGATE compatible task definitions (#34155)

Reverts #33608

This is a breaking change because `cpu` property allows input like `1vcpu` although it's not documented in the public CFN documentation.

This would mean that the reverted PR will cause regression on CDK app that looks like below
```
const taskDefinition = new TaskDefinition(this, 'MyFargateTaskDef', {
      compatibility: Compatibility.FARGATE,
      family: "update-service-test-fargate-taskdef-small-cpu",
      memoryMiB: "2gb",
      cpu: "1 vcpu",
      networkMode: NetworkMode.AWS_VPC
    });
```

Author: GavinZZ