Remove the unused sh4eb target

Remove the unused sh4eb target

Since the "shix" machine has been removed, the "r2d" machine is the only
machine that is still available for the sh4 and sh4eb targets. However,
the "r2d" machine apparently does not work in big endian mode, see here:

 https://lore.kernel.org/qemu-devel/87a5fwjjew.wl-ysato@users.sourceforge.jp/

So there is no working machine left in the sh4eb-softmmu target, i.e. it
is currently completely useless. Thus remove it from the configuration
now. (Note: The linux-user binary is not removed since it might still
be used to run sh4 binaries in big endian mode).

Message-ID: <20240926105843.81385-1-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>