meson: Remove libibumad dependence

meson: Remove libibumad dependence

RDMA based migration has no dependence on libumad. libibverbs and
librdmacm are enough.
libumad was used by rdmacm-mux which has been already removed. It's
remained mistakenly.

Fixes: 1dfd42c4264b ("hw/rdma: Remove deprecated pvrdma device and rdmacm-mux helper")
Cc: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20240611105427.61395-2-pizhenwei@bytedance.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>