How to remove UV information from an object I'm having an issue importing models in to Unity.

When I started modelling I was using UV unwrap to texture the objects.
After a bit of testing I decided to rather use flat materials.

Below you can see the issue. any object that was previously unwrapped keeps this Unwrap info. I cleared the seams, reset UVs and removed the texture from the object.
But still, models such as this rock keep the UV info and remain attached to the original texture material every time I try import to Unity. 
The material rock_01 in blender, seems to import but is renamed in Unity to New Material.

Compare to the trees, which were made later and never unwrapped, they work fine.
Where is this UV information being stored and how can I get rid of it?

Many thanks.
The '-' button in the mesh tab may be what you are after: