anv: remove assert, group can have 0 shaders in it

This seems to be equal assert with febe90e109 as we hit this when
launching Quake II RTX.

Fixes: 69b6b4cb28 ("anv: add shader instruction emission")
Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37429>

src/intel/vulkan/genX_shader.c

@@ -1373,8 +1373,6 @@ genX(write_rt_shader_group)(struct anv_device *device,
                             void *output)
 {
 #if GFX_VERx10 >= 125
-   assert(shader_count >= 1);
-
    switch (type) {
    case VK_RAY_TRACING_SHADER_GROUP_TYPE_GENERAL_KHR: {
       assert(shader_count == 1);