Revert "Implement EXT_discard_framebuffer in D3D11 renderer"

Causes failures in video related WebGL tests.  Either there is a bug in the implementation or how chrome is using it.

This reverts commit b13daa8f79f4d16a990d968d7d2c04da6b72d302.

Change-Id: Ic0d74840c664bf4de18d85cc3ff7f7153936d9b0
Reviewed-on: https://chromium-review.googlesource.com/262715
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libANGLE/renderer/d3d/FramebufferD3D.cpp b/src/libANGLE/renderer/d3d/FramebufferD3D.cpp
index bf9a17e..5bb9681 100644
--- a/src/libANGLE/renderer/d3d/FramebufferD3D.cpp
+++ b/src/libANGLE/renderer/d3d/FramebufferD3D.cpp
@@ -161,6 +161,18 @@
 {
 }
 
+gl::Error FramebufferD3D::invalidate(size_t, const GLenum *)
+{
+    // No-op in D3D
+    return gl::Error(GL_NO_ERROR);
+}
+
+gl::Error FramebufferD3D::invalidateSub(size_t, const GLenum *, const gl::Rectangle &)
+{
+    // No-op in D3D
+    return gl::Error(GL_NO_ERROR);
+}
+
 gl::Error FramebufferD3D::clear(const gl::State &state, GLbitfield mask)
 {
     ClearParameters clearParams = GetClearParameters(state, mask);