Unity 2017.3 does not contain the definitions from the Spine runtime.
Runtime:
spine-unity 4.0 (updated 2022-03-22, changelog)
Compatible with Spine 4.0.00 or newer and Unity 2017.1-2021.1.
However, the SkeletonRenderTexture.cs contains 2 undefined definitions:
Found the script is in examples and I just delete the examples folder and everything goes right.