Also remove traces of cube texture support for OpenGL ES 1.1. We don't
support the OES_texture_cube_map extension, and it would be non-trivial
due to requiring reflective texture coordinate generation.

Change-Id: I5c224f925fc9c03053acaf33e126dae4f3ffe4d9
Reviewed-on: https://swiftshader-review.googlesource.com/16750Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>