flavours: rename meta-python-dunfellplus to meta-python-extra

The repository with the layer was changed in the git-repo manifest
and the GitLab rename happened separately. There is no way to coordinate
this across repositories better AFAIK.

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@huawei.com>

flavours/linux/bblayers.conf.sample

@@ -28,7 +28,7 @@ BBLAYERS ?= " \
   ##OEROOT##/../meta-openembedded/meta-networking \
   ##OEROOT##/../meta-openembedded/meta-perl \
   ##OEROOT##/../meta-openembedded/meta-python \
-  ##OEROOT##/../meta-python-dunfellplus \
+  ##OEROOT##/../meta-python-extra \
   ##OEROOT##/../meta-st-stm32mp \
   ##OEROOT##/../meta-st-stm32mp-addons \
   ##OEROOT##/../meta-av96/meta-av96-core \