Remove riak_core_dtrace

[martinsumner]

Remove riak_core_dtrace. It may well be broken as this PR was never accepted basho/riak_core#926.

Requires removal form riak_kv.

[martinsumner]

May also require changes to Riak CS, as well as documentation changes

[martinsumner]

Note that https://github.com/opendtrace has not had any recent changes. With the growing popularity of eBPF can it be assumed that dtrace needs are unlikely to re-emerge.

Can current tracing needs be met through erlang:dbg?