Generator should not generate those tag related methods for a resource that does not have tags

[ArcturusZhang]

The criteria of generating the tags methods are checking if the resource model has the tags property, but not checking if this tags property is flattened from the properties envolop.
We need to fix this.

[ArthurMa1978]

The new MPG fixed this and we don't need to fix this for autorest.csharp codegen