remove invalid assertion (span->facing may be set because of polygonmode)

src/mesa/swrast/s_stencil.c

@@ -1009,8 +1009,6 @@ stencil_and_ztest_pixels( GLcontext *ctx, SWspan *span, GLuint face )
 GLboolean
 _swrast_stencil_and_ztest_span(GLcontext *ctx, SWspan *span)
 {
-   /* span->facing can only be non-zero if using two-sided stencil */
-   ASSERT(ctx->Stencil._TestTwoSide || span->facing == 0);
    if (span->arrayMask & SPAN_XY)
       return stencil_and_ztest_pixels(ctx, span, span->facing);
    else