A couple of class members from PixelShader and VertexShader
were still public. Fixed that in this cleanup.

Change-Id: I2dfaac7fd4cecdc791f1ef7236148e74c4b5b486
Reviewed-on: https://swiftshader-review.googlesource.com/5850Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>