intel: Always enable GL_ARB_framebuffer_object

intel: Always enable GL_ARB_framebuffer_object

Now that _mesa_BindFramebuffer does the right thing in ES contexts when the
gl_extensions::ARB_framebuffer_object bit is set, the Intel driver doesn't
need this hack.

No piglit or GLES2 conformance regressions observed on IVB, and this
patch (and the previous) fix es3conform's framebuffer_srgb_draw and
transform_feedback_misc tests.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>