docs/about/deprecated: Remove empty 'related binaries' section

Commit 497a30db ("qemu-img: Require -F with -b backing image")
removed the content of the "Related binaries" section but forgot
to remove the section title. Since it is now empty, remove it too.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Willian Rampazzo <willianr@redhat.com>
Reviewed-by: Yanan Wang <wangyanan55@huawei.com>
Reviewed-by: Joaquin de Andres <me@xcancerberox.com.ar>
Message-Id: <20211105142656.145791-1-philmd@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

docs/about/deprecated.rst

@@ -370,9 +370,6 @@ The ``I7200`` guest CPU relies on the nanoMIPS ISA, which is deprecated
 (the ISA has never been upstreamed to a compiler toolchain). Therefore
 this CPU is also deprecated.
 
-Related binaries
-----------------
-
 Backwards compatibility
 -----------------------