Remove deprecated target tilegx

TILE-Gx was only implemented in linux-user mode, but support for this CPU
was removed from the upstream Linux kernel in 2018, and it has also been
dropped from glibc, so there is no new Linux development taking place with
this architecture. For running the old binaries, users can simply use older
versions of QEMU.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Acked-by: Richard Henderson <richard.henderson@linaro.org>
Acked-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20210224183952.80463-1-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>