vc4: Remove vestiges of alpha test lowering.

We stopped reporting the alpha test screen cap, and stopped using the
value in the key, so now shrink the key.  This gets another switch case
out of the hot uniforms upload path.

Fixes: 1404b8b1e5 ("vc4: do not report alpha-test as supported")
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8601>

src/gallium/drivers/vc4/vc4_program.c

@@ -2742,10 +2742,6 @@ vc4_update_compiled_fs(struct vc4_context *vc4, uint8_t prim_mode)
         key->stencil_full_writemasks = vc4->zsa->stencil_uniforms[2] != 0;
         key->depth_enabled = (vc4->zsa->base.depth_enabled ||
                               key->stencil_enabled);
-        if (vc4->zsa->base.alpha_enabled)
-                key->alpha_test_func = vc4->zsa->base.alpha_func;
-        else
-                key->alpha_test_func = COMPARE_FUNC_ALWAYS;
 
         if (key->is_points) {
                 key->point_sprite_mask =