binutils/sstrip: mark as obsolete

sstrip is causing more trouble and grief than tolerable.
It is broken at least on PPC. It does not build on non-ELF
systems (eg. mingw32, MacOS-X...). Plus, it is easy to
install.

Hide it behind OBSOLETE.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

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