The Extra Sampling is retained in the Model and cannot be removed, but if you remove the requested Extra Sampling, you can then open the Total Model in the Surface Manager and click to Build the Surface.
The Surface observes the removal of the extra Sampling and restores the Triangulation to match the standard + requested Sampling.
Rebuilding the Model will re-apply the extra sampling so be sure to then rebuild the Surface as well (they are not the same thing).
It should also be noted that Vertical Curves automatically get a 1.0m spacing as set in the Settings > Cross Section Usage tab > VC Spacings entry.
