Remove default value for required uri property.

[michael-simons]

The auto configuration of the driver is conditional:

@ConditionalOnProperty(prefix = "org.neo4j.driver", name = "uri")

We do this so that this starter doesn't clash with the current Spring Data Neo4j starter you get on start.spring.io.

If we would default to localhost, than the user would end up with a connection configured through SDN/OGM and this starter.

If the user adds this starter here, they have to be explicit in configuring the URL.

By doing so, it will than override the auto configuration of SDN/OGM.

Currently, this is not clear, as we a) don't mention it clear enough in the docs and b) default the URL in the properties.

cc @JMHReif