poky.conf: prune SANITY_TESTED_DISTROS

Remove several old/untested distros from the list:
* poky-1.8 and poky-2.0 are no longer supported releases
* ubuntu-14.04 is an LTS but we plan to remove it from the
  project's autobuilder cluster as the kernel is old and
  it doesn't use systemd -- therefore this will no longer
  be tested.
* ubuntu-14.10 and ubuntu-15.10 are no longer supported
* fedora-22 and fedora-23 are EOL
* opensuse-13.2 is discontinued

Add opensuse-42.2, it's the openSUSE version we run on the Yocto
Project autobuilder cluster.

The distro support plan is documented on the Yocto Project wiki:

https://wiki.yoctoproject.org/wiki/Distro_Testing_Plan

they are easily summarised as:
- Fedora: most recent 2 releases
- Ubuntu: most recent LTS and latest release, unless they are the same
  in which case the most recent 2 releases
- CentOS: latest release
- openSUSE: latest release

(From meta-yocto rev: ba5ad19cbe9066823fe3a3b432a893f4cf67be47)

Signed-off-by: Joshua Lock <joshua.g.lock@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-poky/conf/distro/poky.conf

@@ -70,24 +70,17 @@ https://.*/.*    http://downloads.yoctoproject.org/mirror/sources/ \n"
 CONNECTIVITY_CHECK_URIS ?= "https://www.example.com/"
 
 SANITY_TESTED_DISTROS ?= " \
-            poky-1.8 \n \
-            poky-2.0 \n \
             poky-2.1 \n \
             poky-2.2 \n \
-            ubuntu-14.04 \n \
-            ubuntu-14.10 \n \
             ubuntu-15.04 \n \
-            ubuntu-15.10 \n \
             ubuntu-16.04 \n \
             ubuntu-16.10 \n \
-            fedora-22 \n \
-            fedora-23 \n \
             fedora-24 \n \
             fedora-25 \n \
             centos-7 \n \
             debian-8 \n \
-            opensuse-13.2 \n \
             opensuse-42.1 \n \
+            opensuse-42.2 \n \
             "
 #
 # OELAYOUT_ABI allows us to notify users when the format of TMPDIR changes in