Framebuffer related code is being implemented properly
in VkSurfaceKHR.cpp and related files, so old OpenGL
framebuffer code can be removed to avoid confusion.

Bug b/124265819

Change-Id: I08a87c17e8b029c6f82d252e1ff1ef810ab200ae
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/27108Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>