poky.conf: remove Ubuntu 21.10

Ubuntu 21.10 is no longer updated by Canonical
and since 22.04 is available and supported, it's
no longer useful to test it and declare it as supported.

(From meta-yocto rev: 8f8bde4f5a9b37d3a93615c22b1896fd47973478)

Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-poky/conf/distro/poky.conf

@@ -38,7 +38,6 @@ SANITY_TESTED_DISTROS ?= " \
             poky-4.1 \n \
             ubuntu-18.04 \n \
             ubuntu-20.04 \n \
-            ubuntu-21.10 \n \
             ubuntu-22.04 \n \
             fedora-34 \n \
             fedora-35 \n \