docs(*): Remove Cassandra from Readme
Remove cassandra from the Readme as it isn't a supported provider anymore.
Spinnaker Application & Project Metadata Repository
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-This service fronts a Spinnaker datastore. By default it's Cassandra, however, it's intended that any datastore could work. Front50 written using [Spring Boot][0].
+This service fronts a Spinnaker datastore. It's intended that any datastore could work, there are a number of current storage providers. Front50 written using [Spring Boot][0].
### Debugging
