fbo-integer: Remove the invalid DrawPixels test.
Quoting the error that we trigger in Mesa:
/* GL 3.0 introduced a new restriction on glDrawPixels() over what was in
* GL_EXT_texture_integer. From section 3.7.4 ("Rasterization of Pixel
* Rectangles) on page 151 of the GL 3.0 specification:
*
* "If format contains integer components, as shown in table 3.6, an
* INVALID OPERATION error is generated."
*
* Since DrawPixels rendering would be merely undefined if not an error (due
* to a lack of defined mapping from integer data to gl_Color fragment shader
* input), NVIDIA's implementation also just returns this error despite
* exposing GL_EXT_texture_integer, just return an error regardless.
*/