eglCreateContext: Remove the check for whether config == 0

eglCreateContext: Remove the check for whether config == 0

In eglCreateContext there is a check for whether the config parameter is zero
and in this case it will avoid reporting an error if the
EGL_KHR_surfacless_context extension is supported. However there is nothing in
that extension which says you can create a context without a config and Mesa
breaks if you try this so it is probably better to leave it reporting an
error.

The original check was added in b90a3e7d8b1bc based on the API-specific
extensions EGL_KHR_surfaceless_opengl/gles1/gles2. This was later changed to
refer to EGL_KHR_surfacless_context in b50703aea5. Perhaps the original
extensions specified a configless context but the new one does not.

Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>