Parameters show up in material instances even if they're not supposed to be exposed

In this case, I've added inputs to a material function. That material
function input uses a parameter as it's default value.

[image: Inline image 1]

When referenced in the shader
[image: Inline image 3]

Both the default input parameter and the new parameter show up instead of
just the override parameter.

[image: Inline image 2]

Repro steps:

1. Create a Material
2. Create a Material Function
3. In the Material Function, add a Function Input and set it to Scalar.
4. Add a new scalar parameter and call it "Test_01". Plug it into the Preview input of the function input
5. Plug the output of the function input straight into the output node of the Material Function
6. Add the Material Function to the new Material
7. Create a new scalar parameter and call it "Test_02", which you plug into the input of the Material Function
8. Plug the output of the material function into Base Color
9. Compile
10. Create a Material Instance from the Material.
11. Observe that both Test_01 and Test_02 parameters are visible, even though Test_01 doesn't really get applied to the final result.