panvk: Advertise VK_KHR_shader_relaxed_extended_instruction

Handled by common code.

Signed-off-by: Mary Guillemard <mary.guillemard@collabora.com>
Reviewed-by: John Anthony <john.anthony@arm.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Part-of: <!32131>