In order to delete texture you need to bake it first with "Bake Substance Texture" button (red icon over the texture slot would be gone).
But for some strange reason that button is grayed out while displacement texture in selected for *some* of the substances.
Like those bricks...
This is older version of iClone, where "Bake Substance Texture" was available to Bake a Displacement texture
And here is a Current release, where it is grayed out
NOTE: It works as expected with Substance Power 200, but not with Substance PBR 200
Must be a bug.