Add features classifier to Maven artifact for features file and skip cross-build

[gertv]

The features file is published as mvn:io.guanaco.camel.redis/features_2.12/0.9.1/features_2.12-0.9.1.xml.

This seems to break GPR - that artifact is not available for download afterwards. As an experiment (and because of convention), we could try if that is fixed by these two changes:

• Add the features classifier
• Remove the _2.12 cross-build, we already have a separate feature for the _2.11 variant