zipkin-reporter-brave implementation has a sneaky dependency on zipkin2

[codefromthecrypt]

I noticed that zipkin-reporter-brave still has a dependency on io.zipkin.zipkin2:zipkin because AsyncReporter and Sender extend zipkin2.Component among other things.

AsyncReporter

import zipkin2.Call;
import zipkin2.CheckResult;
import zipkin2.Component;
import zipkin2.Span;
import zipkin2.codec.BytesEncoder;
import zipkin2.codec.SpanBytesEncoder;

Sender

import zipkin2.Call;
import zipkin2.Component;
import zipkin2.codec.BytesEncoder;
import zipkin2.codec.Encoding;

We can't avoid a runtime dependency on io.zipkin.zipkin2:zipkin until some alternative surfaces. One way could be to extract simpler generic types that supports both brave and the old call sites without the Call abstraction.

[codefromthecrypt]

when this is done, we should update here as cassandra's jar went from 200->420k for reasons including this https://github.com/openzipkin/brave-cassandra/edit/master/cassandra/README.md