CI: align with Poky

Originally we customised the CI build for speed, by switching to ipkg
instead of rpm for the packages and disabling graphical output support
in qemu-system-native.

These are admirable goals, but more admirable is sharing sstate and
people may wish to use the output of this CI without having to make the
same alterations.

Drop these two changes so that our configuration matches poky. I've
verified that with this change, a build of core-image-sato for qemuarm64
can be built almost entirely from the autobuilder's sstate[1].

[1] gator-daemon, opencsd, and perf are built as these are not built on
    the AB in this configuration.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>

ci/base.yml

@@ -31,8 +31,6 @@ local_conf_header:
     CONF_VERSION = "2"
     BB_SERVER_TIMEOUT = "300"
   setup: |
-    PACKAGE_CLASSES = "package_ipk"
-    PACKAGECONFIG:remove:pn-qemu-system-native = "gtk+ sdl"
     PACKAGECONFIG:append:pn-perf = " coresight"
     INHERIT += "rm_work"
   extrapackages: |