Support for anisotropy in VoxelGI was removed during its development due to the high cost. This was a leftover from anisotropy support.
* GIProbe is now VoxelGI * BakedLightmap is now LightmapGI As godot adds more ways to provide GI (as an example, SDFGI in 4.0), the different techniques (which have different pros/cons) need to be properly named to avoid confusion.